Here's what's great about that matrix:
1) You're starting off with a decent prize anyway, so even if you don't build the bank (and really, how often did someone win the front game without a 7-for-7?) that's $10,000 anyhow.
2) It rewards good front game play further than just getting to play the bonus
3) It gives an asthetically pleasing amount, and it could be handled easily: "You had two category sweeps in your victory, which means we add $10,000 to your bank. For $20,000, here is your first subject..."
The thing about $1,000 per point is the same issue with Bullseye on Family Feud; it gives you TV un-friendly numbers, like a $19,000 bank.