what is the best buy-in to gain MTT experience

I kinda like MTT's and I do OK in low buy in STT's ($5 and $10) so I don't mind using some bankroll from time to time to gain some MTT experience. I've got a couple of questions......

What buy in gives the best 'bang for buck' if I'm looking to gain experience playing in MTT's? On one hand you have the low buy-in ($1) or freeroll ones so I could play loads of them. However I'm put off by the huge fields and the number of people who go all-in on every hand because well, it's only a buck, and if I just double through 13 times I've got every chip in the game!

The larger buy-in ones ($10 level lets say) seem to have fewer players, which I like the idea of, and more sensible play but I have the problem of not being able to fund a huge drain on my bankroll of say 20 MTT's out of the money (quite possible as I get used to them I suspect)

So is it better to play lots of 'questionable' quality MTT's or a few of the more expensive ones?

The next question is more about attitude. The few I've played (around 20 I guess) I've had the 'new-boy' mentality of wanting to finish as high as possible. This has meant that I've allowed myself to be blinded away whilst hanging on for those extra 20 places (not in the money of course). At what point do experienced players feel they are getting too far behind the chip leaders and that they must 'open up' a bit to stay in contention?

As they fall out of the money places?
As they fall behind the average chip stack?
As one 'double-up' will not get them in the money?
As one 'double-up' will not give you an average stack?

Thanks and sorry if they are dumb questions.