hey looseness, cool to hear that mixing up strokes is working for you. as you mentioned i used to get shoulder pain when i swam on my own, before i started swimming with a masters team and began doing all four strokes during workouts. i really haven't had any shoulder pain since then and i do think it has something to do with avoiding repetitive stress injury by mixing things up, but also has something to do with having coaches on deck to check poor technique. for example, once i was getting a bit of a pain in my shoulder blade during workouts whenever we would go over 3,000 yds, and when i asked the coach to check out my stroke, turns out i was not rotating enough on one side, causing excessive strain in that shoulder. it was not something that more and varied swimming would have corrected. i needed to fix the underlying problem first. once i did that... no more pain, even as we increased yardage up to 4,500 at times.
anyway, those nyc rec centers are a great deal. i used to swim at one of them before joining a masters team. the water quality wasn't really that bad. the red hook pool is fantastic. (swimming is much more fun outdoors.) the YMCAs i've been to (dodge and mcburney) are not really that great. they keep the temperature too warm (for the elderly and kids) and do not have proper ventilation, but they're convenient.
the best pools are the university ones. columbia has a really nice pool. i've only attended a practice there once, but it was great. nyu's pool is pretty nice too. oh, and asphalt green's pool is really nice. and by nice i mean, not overheated with adequate ventilation to let the chlorine fumes escape!