Did a search and found a bunch of "for-sales" but no answers.

I happen to walk in on a conversation about pulley kits for the black-top sr20det and the discussion left me wondering. I'm always looking for "weekend upgrades" and this might be a good one so i searched ebay and found a bunch of kits for cheap.

Questions:
1. Is a pulley kit worth the trouble?
2. What's too cheap and what's too expensive?
3. I know the pulley kit "free's up" hp and doesn't create it, but is it a noticeable difference?