It depends on the table, but I'd say 25NL, there are maybe 3 good players tops per table. At 100NL, there is 1-2 excellent players, 3+ good players, then a mix of OK and fishy players. You have to hope to get to the fishy players before the others do. This is all relative of course. I think alot of 100NLers that say 25NL is the same as 100NL don't realize that they themselves have adjusted and gotten better to compensate. And therefore they are one of the excellent players. Therefore, it seems like the same amount of fish as 25NL.

Don't move up until you get to $1500 or more. 2k+ is preferable. And don't just base the jump on bankroll. If you are dominating your current level, then move up. If not, then stay there until you are.