So another try to find a shortcut of your(s) (defilements)... :-) at least you give others chances to enjoy the effort of doing merits. If even they would see fruits of answering your questions for you, such as success by your's would be great.
Well then: read, and pay close attention, Eggman, Atma will write and link.
What level of skill permits meditation to release pleasure? How advanced must one be for this effect?
See again the answer to similar question of yours: Lack of Pleasure and Joy.
To have in the objects of reflection, the devotion for them need to be developed.
For having joy in reflecting about ones generosity, moral conduct, virtues like Devas, certain amount of such successful deeds of merits that such is present in one, need be done in faith, in advanced.
It's not possible to gain without having given a cause, having sacrified first. Like no corn if field-work has not been done. Dhamma does not work on borrow, taking first.
Is focused meditation -- i.e. shamatha -- the only meditation conducive to pleasure? Are there meditations more conducive to pleasure?
To gain the pleasure sukkha, reflect again:
The depending co-cessation
[What's the benefit of devotion/gratitude/generosity/moral virtue?]
"Freedom from remorse, Ananda."
"And of freedom from remorse?"
"Joy, Ananda" (pāmujja)
"And of joy?"
"Rapture, Ananda" (pīti, better satisfaction)
"And of rapture?"
"Tranquillity, Ananda." (passaddhi)
"And of tranquillity?"
"Happiness, Ananda." (sukkha)
"And of happiness?"
"Concentration, Ananda." (samādhi)
"And of concentration?"
"Vision and knowledge according to reality."
"And of the vision and knowledge according to reality?"
"Turning away and detachment, Ananda."
"And of turning away and detachment?"
"The vision and knowledge with regard to Deliverance, Ananda."
*see Upanisa Sutta: Prerequisites
One can gain pīti (satisfaction) by turning to asubha, unbeauty objects, yes.
You might look at the answer on What is the logic behind visualization meditation
But since you nature is an aversive, especially starting by lack of compassion to yourself, it's not recommended, given your seek after pleasure, and the insight that aversion migh not be conductive as well.
Again, aside of Dukkha, it seems as if the is not much base for now, so rather to focus on building a palace in a swamp, focus on virture and much, much generosity, = reducing consuming but giv, give up, serve...
Is there still attachment when we want the benefits of pleasure not for themselves, but for an altruistic or wider goal?
Seek after sensual pleasure kills, sensuallity is the reason for killing and wars in this world: How can there be any alturistic be included in such?
But, to do not understand wrong: the pleasure gained by Jhana is said to be outside the sphere of the five strings and such pleasure does not cause remorse if enjoyed.
Don't be afraid of this pleasure!
""...Simply from my eating so little, if I tried to ease my body by rubbing my limbs with my hands, the hair — rotted at its roots — fell from my body as I rubbed, simply from eating so little.
"People on seeing me would say, 'Gotama the contemplative is black.' Other people would say, 'Gotama the contemplative isn't black, he's brown.' Others would say, 'Gotama the contemplative is neither black nor brown, he's golden-skinned.' So much had the clear, bright color of my skin deteriorated, simply from eating so little.
"I thought: 'Whatever brahmans or contemplatives in the past have felt painful, racking, piercing feelings due to their striving, this is the utmost. None have been greater than this. Whatever brahmans or contemplatives in the future will feel painful, racking, piercing feelings due to their striving, this is the utmost. None will be greater than this. Whatever brahmans or contemplatives in the present are feeling painful, racking, piercing feelings due to their striving, this is the utmost. None is greater than this. But with this racking practice of austerities I haven't attained any superior human state, any distinction in knowledge or vision worthy of the noble ones. Could there be another path to Awakening?'
"I thought: 'I recall once, when my father the Sakyan was working, and I was sitting in the cool shade of a rose-apple tree, then — quite secluded from sensuality, secluded from unskillful mental qualities — I entered & remained in the first jhana: rapture & pleasure born from seclusion, accompanied by directed thought & evaluation. Could that be the path to Awakening?' Then following on that memory came the realization: 'That is the path to Awakening.' I thought: 'So why am I afraid of that pleasure that has nothing to do with sensuality, nothing to do with unskillful mental qualities?' I thought: 'I am no longer afraid of that pleasure that has nothing to do with sensuality, nothing to do with unskillful mental qualities, but that pleasure is not easy to achieve with a body so extremely emaciated. Suppose I were to take some solid food: some rice & porridge.' So I took some solid food: some rice & porridge. Now five monks had been attending on me, thinking, 'If Gotama, our contemplative, achieves some higher state, he will tell us.' But when they saw me taking some solid food — some rice & porridge — they were disgusted and left me, thinking, 'Gotama the contemplative is living luxuriously. He has abandoned his exertion and is backsliding into abundance...
"So when I had taken solid food and regained strength, then — quite secluded from sensuality, secluded from unskillful mental qualities, I entered & remained in the first jhana: rapture & pleasure born from seclusion, accompanied by directed thought & evaluation. But the pleasant feeling that arose in this way did not invade my mind or remain. With the stilling of directed thoughts & evaluations, I entered & remained in the second jhana: rapture & pleasure born of concentration, unification of awareness free from directed thought & evaluation — internal assurance. But the pleasant feeling that arose in this way did not invade my mind or remain. With the fading of rapture I remained equanimous, mindful, & alert, and sensed pleasure with the body. I entered & remained in the third jhana, of which the noble ones declare, 'Equanimous & mindful, he has a pleasant abiding.' But the pleasant feeling that arose in this way did not invade my mind or remain. With the abandoning of pleasure & pain — as with the earlier disappearance of elation & distress — I entered & remained in the fourth jhana: purity of equanimity & mindfulness, neither pleasure nor pain. But the pleasant feeling that arose in this way did not invade my mind or remain....
Maha-Saccaka Sutta: The Longer Discourse to Saccaka
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]