Replying to my own earlier post...
My iPad 2 ios 9 started freezing and displaying other weird behavior so I decided I might as well upgrade from ios 9.0 to 9.1. The result is that the iPad is working better than it did with ios 9. it's definitely a keeper. Safari is pretty snappy as long as the web page doesn't have too many animations or popup ads (are you listening Amazon?). And by the way, none of the ad blockers for Safari will work on a 32 bit iPad :-( An additional benefit for me with ios 9.0 or 9.1 is that battery life is much improved, but that may have been the result of the hard reset to factory specs (see earlier post).
The biggest downside to ios 9.0 or 9.1 compared to ios 7 is the delay when switching between apps (sometimes). Switching from Safari to Mail can as many as 10 seconds but it's usually one second or less. However, the overall usability of my iPad with ios 9.1 is fine. And ios 9.0 and 9.1 both appear to be much faster than ios 8. Again, however, I'd say that if you're happy with ios 7 on an iPad 2, don't upgrade unless you really want one of the new features.