how many are actively being developed?
Impossible to say. How do you define “actively being developed”? If a plugin remains compatible through multiple WP updates and, therefore does not need to be updated, should that imply that it is not being tested & maintained?
how many are getting more than a handful of downloads a month?
What does that have to do with anything? A plugin that effectively meets the needs of only 6 users a month is no less valuable than one that is downloaded hundreds of times a month. Niche plugins are no less valuable than their more common brethen.
I seriously doubt those even work with WordPress 3.3.1
You think? I’m using a plugin on my 3.3.1 sites that hasn’t been updated in almost 3 years. and it still works perfectly.
I am hoping to find a list of featured plugins (actively developed & popular) that do work.
And you’re not going to find one I’m afraid. As I’ve tried to illustrate, the reality is not quite as black & white as you seem to think. The only way to do this is to to start testing plugins manually in as many different server environments as possible. And then re-test them all every time there is a WordPress update.
Would you want to take that on? I know I wouldn’t ??