In some cases DLC is fair. I believe GT5 handled DLC fairly. The game was in production a good amount of time, and the DLC was likely not able to make it in once the game went gold and was produced afterwards.
However if you've played any of the NFS's including The Run, Hot Pursuit, or Most Wanted (not to include many other games out there), you'll know what I mean about DLC being handled poorly. Some developers are literally giving what feels like half a game and tacking on the DLC after the game release in order to get the "Complete Version". Even GRiD 2 already has over $30 in DLC and it just released. Not cool...
Now in the case of GT6, I have a dilemma. I've already paid for GT5 at least 3x over (Collectors edition, XL edition, Car Pack 2 + 3, Suits, 3 Paint packs, Spa, Racing Car Pack, & Route X), so having these things in GT6 may be cool, but I've already paid for them, so it doesn't feel like such a huge bonus for me and is more or less expected. From what I know, there's new physics (update), a few new cars (15% New Game/ GT5 DLC), and a couple of new tracks (25% New Game/ GT5 DLC), oh and some GPS ghost lapper that only a handful will be capable of using. This equates to me as 30% to maybe 45% of a new game to me, with the rest being either rehashed, updateable, or DLC-able (IMHO mind you).
From what I've seen so far and with 3 years under the belt, it seems like MOST of the new content is being held for DLC with GT5 getting a few tweaks, and polishing in the process (and becoming GT6). As of yet, personally, I'm not sold. And I feel that as long as we keep buying into PD's/Kaz's/these DLC trends, we're never going to get a fully overhauled and up to date GT. Like a tough love of sorts, I wish for GT to improve and I feel that as long as we continue to fatten their wallets regardless of the reheated leftovers they continue to serve us, we're never going to see the GT we're hoping for.
Now mind you, I do understand we still don't know everything of GT6, and there may yet be much to be revealed. So I could be mistaken. But as of yet, I'm not impressed, and GT6 is lingering in a "No-buy" status for me. However I can't wait. 11 days until E3!