Enterprise could look as good as TNG if they rescanned the negatives and re-rendered the CG but that isn't going to happen, like you said it looks really good so why spend a lot of money to make it better when most will already be happy with how it looks now.
CBS doesn't want to spent lots of money on making the Blu-Rays for something they know will have low sales.
Is this foreshadowing for the DS9 and VOY releases?
As I have repeated before, it is hard to read CBS' relative lack of investment in Enterprise
as indicative of what the studio would do for Star Trek: Deep Space Nine
or Star Trek: Voyager
was mastered in HD. The other spin-offs were mastered in SD. There is no way for CBS to put out the same half-assed product.
was the least popular live action Trek series. As such, it is hard to guess what CBS will do with the other series based on this one.
I tend to agree with your reasoning for the most part. But what makes me wonder about the amount of money that CBS will be willing to invest in DS9/Voyager is the fact that both seemed to struggle in strip syndication.
Neither series seemed to have much life after their first runs here in the States.