Different people have different price points they're comfortable with, and if this isn't yours, that's certainly alright.
That said, I don't think it's entirely accurate to characterize GT on release as "half a game." A lot of early access games on release are VERY incomplete, with major mechanics, assets, story stuff and so on missing, severe bugs, and so on. GT on the other hand was a fully-functional game. You could play it all the way through, all the necessary mechanics were there, as well as most of the story, and bugs were minimal. Yes, there were extra scenes hinted at that weren't there yet, but the game was perfectly enjoyable in its original state. It's not a perfect divide either way, since with this first pack especially there were a few scenes and narrative bits that were needed overall, since the full corruption route is part of the story, but I see these packs as leaning more toward DLC or expansion packs than missing chunks of the original game. If I hadn't left those narrative hints in the initial release that there was going to be more stuff, most people wouldn't have even noticed.
In general, it's important to me to only charge for stuff as it exists, which is why I've settled on this structure. I definitely don't want to get in the habit of taking people's money before a game exists (outside of Substar, but that's a different situation). The "ideal" solution would be getting a massive loan from some absurdly wealthy friend, spending 2 years making each game to completion, and then releasing it. This is how medium-sized games were traditionally made (just replace "friend" with "investor" and replace loan with getting a cut of the action). But barring that, I have do things in chunks, as the funding works out. That said, it's been working fairly well so far, and hopefully will continue to.