Which sounds all well and good, but you cannot get clear or affective results from such a skewed audience. They already believe and want the outcome to be good as opposed to being fair and subjective.
They believe in the gameplay concept. They may not believe in the current implementation. You have a group of people who aren't going to ask for radical rewrites, but instead are going to ask for minor changes to help polish the gameplay. You'll already notice people who have ideas that they want to have changed. Also, becuase they want the outcome to be good, they'll be much more likely to put in the work to make it good and to keep their suggestions in the realm of implementable changes rather than suggesting drastic changes.
going want the game to be what *they* want out of it as opposed to what what might be balanced or effective in terms of giving the game a mass appeal.
Not something I noticed. Everybody wants something different from a game, so why is the group of people with preorders different? In the sins beta, rather unsurprisingly everybody wanted the game to be balanced, and the resulting game was relatively well balanced (discounting a cheap trick that wasn't as easy in beta and a few issues with the advent, who we'd never seen). It's not like people who buy all for some reason hate balance.
Now don't get me wrong, I think rewarding preorders with a beta key is great, but seeding your testers to be ONLY those people will leave you with yesmen and many patches and fixes post release when your player base evens out.
You should've seen the amount of unholy hell pathfinding in early versions of sins got. Nothing of the sort you talk about happened.