I agree, the level 10 kit is the best thing to happen to mags since N2. Other than that stock is best. Aftermarket mag bolt are usually of inferior quality and do nothing to improve performance.
Absolutely - I've got a classic mag with a foamieless bolt and it's never chopped, so even a good level 7 set up will see you fine if you stick with the AGD products.
However, if you have an RT or E-mag (with considerably faster rates of fire) or are finding that you do break paint, then lvl 10's where it's at. Check out Automags.org tech forum for all the details.