My advice wasn't exactly solicitted, but I give it anyway. O_o
I suspect that you may have sub-consciously posted this because you almost wanted your enthusiastic user base to "talk you into" laying the extra dosh down on the table, but only because you knew which way you were leaning, and you were feeling a bit of a crush on your dreams. Your logical, thinking mind knew what would be the wisest course of action, and yet your creative passion wouldn't settle for it. It's understandable. : /
Most people have jumped to the task admirably, and as I'm sure you knew, at least in the back of your head, they're gungh-ho about the whole thing, and are all for plowing ahead. I think you wanted them to energize your impulsive passionate side enough to overpower your logical, cautious side. Of course, if you were to look at my wall, you'd notice a patch of blank space where a degree in psychiatry should be, so I'll stop practicing without a license (or even, really, the slightest bit of education) for now. ;)
I'll tell you what I think you already feel for yourself. I'm probably wrong about that, but the advice itself still stands:
If you're still functioning fairly well as you are, working from your collective homes, or your basement, then I'd say it'd probably be an unwise move to invest such a considerable amount of money in an upgrade that may be largely unnecessary, at least as of YET. There's no point in maintaining a mega-stadium that can seat 100,000 when the home games usually only yield 10,000 fans, right? In a situation like you had originally, where you could have gotten lucky and had the building for a reasonably low price, it may have been worth it...sometimes an upgrade, or a move up, can actually PROMPT growth, which is what you said you were after. You're feeling frustrated because the sort of energized, productive environment you want to create is difficult to maintain in something as modest as your basement. The situation is understandable.
A premature upgrade, however, could also inhibit growth...biting off more than you can chew is something to be avoided. I'd say that in most cases, it's better to wait for the growth before climbing a costly rung of the ladder, rather than taking a risk and climbing that rung first, merely hoping that the growth will inevitably follow, and thus make the step up worth the cost. The growth is happening, and that point will come; Newgrounds is getting bigger and bigger, every year. Rushing to that point, however, when you don't exactly need it quite yet, could mean a fatal stumble.
Then again, what do I know? Do what you feel is best, and I'm sure whatever the eventual outcome of your decision, everything will be okay.