I came from Forza (1, 2, and 3). The thing is, the DLC in Forza Motorsport is generally (not speaking for 4, haven't played) Turn10 releasing stuff that was available in the collectors edition or VIP members. Not only this, as soon as they started working on Forza 4 (some 3 to 4 months after the release of 3) the dlc slowed down immensely, and VIP members were no longer receiving a car every week, as they were supposed to for purchasing the collectors edition.
This is the main reason I switched to GT5, as they are consistent, at the very least. Turn10 decided to make everything available to the non-collector purchasers, at roughly 20 dollars less then the collectors edition cost, as well as not hold up to the included perks of the collectors edition. I wouldn't complain about Forza having regular DLC, because in the end, they tend to screw over their customers.
Now, I do agree, I wish for much more DLC, only because well, hell, there are still a lot of cars I would love to have. More freedom of modification is somewhat of a definite must in my book. At the very least, motor swaps should be possible (the fact that the 240zg can't have forced induction or an L28 swap is aggravating as hell to me), but I would like to see more modifications all around. More visual additions would be fantastic, especially for standard cars. I don't know about you, but the 3 generic fast and furious spoilers they have available don't really do it for me aesthetically. All in all, I don't see any issues with what you have listen, in fact, I'm definitely in.
TLDR; Sign me up - RogerIsJolly