I don't look at it as money vs quality. I see it more as, more quality more money. So start with quality.
The only way to make money is if people play your games. The perceived value of your games is higher, and the amount of interest is higher when you make good games.
One thing Valve has, probably more than any other game company (besides possibly Zynga) is a ton of data on gamer behavior across all their titles.
They've looked really hard at how players interact on some of their AAA titles like Team Fortress 2 and Left 4 Dead, and more recently on Portal 2. They know how people play, and what they're willing to spend on.
Seriously, they are running EEG brainwave scans and pupil dilation tests on gamers during play testing to understand how their games are effecting their players. That level of customer understanding makes it pretty easy to know where and how to turn the money machine on.