The whole point of AA is to get all-in preflop and I don't think you should ever pass up an opportunity to do it. In an SnG there is absoluetly no reason to get "fancy" and just make a normal re-raise to get more chips in the pot, just push and you will be called most of the time by the original raiser/reraiser who's either got AK or a pair.

The play in teh first hand was very poor since you're building a big pot (good) with loads of players (bad). The pot is big enough when action comes back to you for you to want to take it down, if you go all-in and everyone folds, that's a good result, if they call, that's good too. If you do what you did, you're giving them a chance to outdraw you, and you're committinmg yourself to the pot out of position.