There are lots of questions you addressed and I will try to touch on as many as I can. Please be aware that my background and area of expertise is not in Buddhist texts, but the process of insight. We may have very different definitions of particular words and concepts, but I believe I may have information that may ring true in your own life.
My understanding is that realizing enlightenment is universally desirable.
What is desirable is completely dependent on the mind who wants it. I am sure there are many people who have walked this earth who have had extreme aversions to deep insights. The reason most people are not enlightened today is because of personal desires and aversions.
I interpreted what you said above as perhaps enlightenment is "universally beneficial" or "brings universally positive effects".
The "value" of enlightenment and the mental states that occur afterwords can not be derived. Only the mind of the illusory self is capable of making such judgements.
When it comes to what happens to arahant after death, my understanding is that Buddha did not give a very concrete answer.
I can not speak about the texts that outline the Buddha's words, but I can only speak of my own experience.
We are getting into very indescribable territory here, so please do not take anything I say here at face value. I will wrap statements that are untrue, but the best i can do, in italics.
"it falls under the category of things that are not known"
This statement is neither true, nor false.
It is not true, because although what happens after death can not be known by the mind of the illusory self, it can be known by what lives beyond the mind.
It is not false, because only the mind is capable of knowing. What lives beyond the mind is not capable of knowing.
*It is only once the answer is seen by what is beyond, that the mind can begin to use words and concepts to (poorly) explain the non-explainable.
"the answer will not end suffering so it is irrelevant”
Irrelevant is not the word I would use here. What the statement is attempting to address is how the question is poorly formatted. Let me explain with an example. Say I ask this question:
"Why can't I see the second sun in our solar system?"
The question is asking about visibility. The problem with the question is that it is completely dependent on a belief in the existence of a second sun. The question has no answer because the principle understanding it was based on was untrue.
When asking the question "What happens to an arahant after death", you are asking about a being that does not exist. To be clear, I am not saying that there are no arahants, I am saying that there are no "separate illusory selves" that are capable of death.
"The Illusory self" is perpetuated by "The Mind". The Mind is a non-existent entity that operates with the sole purpose of ascribing agency to transient sensations that are fundamentally "not self".
Very simply put, the self you believe yourself to be is an illusion. An illusion can not die. Take the example of a mirage. A mirage does not exist as a separate entity. It is simply an illusion that has been mistaken for water. Once you walk closer and see there is no water, the misjudgment is known clearly. Just as you can not walk up to and destroy a mirage, you yourself can not die. Not because you are immortal, but because the concept of death does not apply to a non-existent entity.
But isn’t happiness generally considered a pleasant feeling?
What is pleasant, and what is unpleasant is completely dependent on interpretation.
Can you imagine a situation where you felt happiness, but believed it wasn't the appropriate response? Happiness and sadness are both equal candidates for desire and aversion. There are many who believe they deserve to be unhappy. There are many who believe they are "bad people" for taking joy in something they "shouldn't".
And aren’t some non-arahant more happy than they are sad in life? I’m not saying I’m one of those people, but don’t those people exist? So for them, perhaps an endless cycle of death and rebirth isn’t that bad?
Perhaps think about the cycle of death and rebirth not on a macro scale (over lifetimes) but on the micro scale. Who we believe we are has changed over the years. When we were children, we thought of ourselves differently than we do now. We now like and dislike different things. We believe we are constantly evolving and changing. If you buy into that belief, you are unknowingly placing a mask over your own face while looking in the mirror. Some people have a blessed life, and enjoy the face they see. Others, do not. Either way, it is not your face, and there is nothing quite like the overwhelming love and adoration you feel when you see your true face for the first time.
Life can be net-positive in happiness for some, can’t it? For those people, does it make sense to exit out of this endless cycle of mostly-pleasant life and instead enter....nothingness? The unknown? Become an extinguished flame?
What lies behind the mask of the illusory self is not nothingness as you currently understand it. It is sometimes described as "nothingness", but I do not like this description as I feel it only describes 1% of reality. From the point of view of someone who exists, nothingness can be terrifying. Let me attempt to explain the explainable, what is behind the mask.
When you look behind the mask, you see what you have always seen. The difference is, there is clarity in what is seen. It is unfiltered through belief and preconceptions. You only see what is. Many people talk of the concepts of "Creator" and "Creation". What is behind the mask is a contradictory separate union of these concepts. I will call this entity, Being. Being is the creator of all. Being is all that has been created. Being is the one who has been experiencing all your life. Being is the experiences you have been observing. Being is the creator of all concepts. Life, death, happiness, sadness, somethingness, nothingness, layperson, arahant, are all derived from Being. Nothingness, as you know it, can only be known through Being. Being is nothingness and everything else. Being is only unknown by the illusory self. Being can only be known by Being which is what you truly are. Enlightenment is not the extinguishing of a flame, but the absorption of the flame into the most brilliant and amazing star.
But what if I’m not suffering all that much? What if I have a pretty peaceful, happy life? Does it make sense for me to say “yes” to that genie?
Your peaceful, happy life will not end when you say yes. You will realize your peaceful, happy life has no end! You will no longer cling to happiness and see how there is amazing beauty and enjoyment to be found in all emotions.
Do you wish to discover you are undying? Do you wish to discover you are complete? Do you wish to discover you can not be harmed? Do you wish to discover you are beauty? Do you wish to view the world from a place of unity? Do you wish to know who you truly are?
If you answered yes to any of those, this path is for you. The fact you are here, asking these questions means the ball is already in motion. It is only a matter of time, brother, until you see what can not be seen.
From the bottom of my heart I wish you well on your journey. Nothing brings me more joy than the knowledge that you will get there soon. I hope some of what I wrote resonated with you, and if not, I pray you find what does. With love.