What are good strategies for not losing sight of the novelty and nontriviality of one's work?
You are not the only researcher who experiences this. Certainly I personally also do.

It sounds to me like your question is whether these feelings of overexposure to your own work are: 


pathological--the result of some psychological process which makes you feel disenchanted with your old papers, regardless of their actual merit--or:
simply accurate--that is, as time passes, you come to have a more accurate appraisal of your own papers.


You already have suspicions about which of these two possibilities is actually correct. Personally, I try not to second-guess my own negative feelings about myself, so here is a strategy which I have found totally avoids the need to decide between possibilities #1 and #2: by working on a massive, multi-year, very ambitious project which requires many, many papers to develop, explain, and "make good on", I find that my feelings of overexposure about my own old papers, my own looking-at-my-old-papers-and-immediately-seeing-everything-I-could-have-done-better, those feelings are overcome by my excitement for the future of this broader long-term project and the small piece of that project that each of those imperfect papers puts into place. Being able to say to myself "I wish I would have written that old paper more elegantly, or proven this stronger result," or whatever, these feelings are washed away by the feeling of "That paper, no matter how wretched and ugly, still allows me to carry out the next step in the broader project," and then I can live with having written it. Maybe this approach can work for you too.