I try to maintain mindfulness in daily life and I find that most of the time my thoughts keep wandering and I often find myself regurgitating on some random topic which is not at all useful at the moment. Is there any sutta in which Buddha talks about thoughts - which thoughts are useful to dwell on and which are not?
This is restlessness, or the mind being scattered by many thoughts coming and going. Refer to the suttas on the hindrances, e.g.: (Nīvarara) Sangarava Sutta, Nīvarana,pahana Vagga. This is aggravated by Vipallasa (see Vipallasa Sutta). (These could lead to wrong conclusion and views hence keep the Samma,ditthi Sutta in mind.) Also see: Nīvaraṇa an essay by Piya Tan
Thoughts are generally not good to dwell on unless they are directed at maintaining properly executing our daily activities and also perhaps some planning the activities and future. This cannot be avoided if you are householder. Also keep your thoughts on on what can be considered compatible or at least not contrary to Right Thoughts (Samma Sankappa). Thinking lead to concept proliferation and verbal fabrications which is at best avoided when possible at least during a formal meditation sitting.
With regard to concept proliferation the following essay highlights how thinking leads to fabrication: Papañca-Saññā-Sankhā, Concept and Reality in Early Buddhist Thought by Bhikkhu Nanananda. Also Madhu,piṇḍika Sutta covers the topic: perception and mental proliferation. Also Mindfulness in Early Buddhism, by Tse-fu Kuan contains though proliferation in the context of Vipassanā which might be an interesting read.
Buddha don't want to you to cling to anything. There is no classification as worth dwelling or letting go. Just don't cling on any thought thats what we are learning we are not seeking anything we are just being in the moment as it is consciously. Classification is the way of cunning mind. Mara. We are are here to be no mind. Even trying to attain no mind is a seeking. Just be here and now always.