I have no problem paying for more content for the games I like. In the past console games died after a couple of months because of lack of support and it's a nice thing not seeing your favorite activity getting stagnated.
Plus it's not like I'll cry over $100, especially considering how much there's already invested on the system (ps3, gt5, gt5 dlc, gt6 disc, wheel, cockpit, various related hardware that's not strictly supported nor bought for the ps3/gt6). I'd cry over lack of tracks though, which is not going to happen since there are lots coming.
The discussion does not revolve around quality against quantity. That's more related to iracing against gt6 really (at least 5 times more expensive, all things considered). What matters here is that there will be dlc, which makes some people feel ripped off while others are happy to pay for more. After all the GT fanbase is very content hungry, quantity over asking for the best quality possible.
edit: There is a sad side to the story though: PD will obviously release a "XL" version that includes all DLC up to that point, both for the ps3 and for the ps4, which will cost only a fraction of what people paid for it. I understand there's the benefit of having early access to content, but an eventual ps4 release (improvements to the core game) with everything on it (content) pretty much means a slap to the face to ps3 customers.