Rehashed BTS? By that you mean one feature they're adding in G&K has the same name but works entirely differently? Unless I'm misunderstanding you, this is sort of like saying CiV vanilla is just a rehashed CIV because they both have combat and world wonders. Or that IV is a rehash of III, III a rehash of II, and II a rehash of I. I doubt you'll find many people voicing those complaints, or saying that that makes Civ II a worse product than if it would have had no gameplay elements carried over from its predecessor.
I understand you may be coming at it meaning that since the two expansions add the same content over the vanilla game (in which case, I'd like to point out that only espionage is ported over; religion was in the stock game in IV), but if that's your concern, I guess my question is "So?" They're both capable of being very good gameplay elements that take some focus off war, which CiV vanilla overemphasizes a chief complaint by the community. If you're saying you wish they would have added something else instead of two new gameplay elements, revamped city-states, new wonders, new scenarios, and 9 new civs, what would you have rather they added? Am I correct that your argument is that you think they should have added more, or wish they didn't add the same things they added in BTS? Because only one of those features was actually also added in BTS, and the other features you mentioned I'm sure nobody is complaining that they added. Can you imagine the outcry if they didn't add new civs and wonders? I guess generally I'm just trying to figure out what you think they should have done.
Also, the last official patch for BTS was released in June 2009, roughly 4 years after CIV was released and 2 years after that expansion came out. I don't know where you got the "they'll probably just support V for another few months" idea. Do you have any basis for that? It seems to me that as long as it's selling well (it is), they'll have people working to produce content, and as long as they're doing that, there will be updates. So if your concern is that all the features they added meant less time working on core AI problems that will never get fixed because the game will get dropped in two months, I'd have to say there's very little to support that. Perhaps you can enlighten me? On top of that, saying CiV vanilla won't get any more patches doesn't hold up if you're going by the franchise history either CiV vanilla's last patch was in July 2007. Warlords came out in July 2006. So there was another year's worth of patches that didn't depend on expansions.
It seems like you're making a lot of assertions that you can't really back up or maybe can, but just haven't yet. TBH this kind of comes off as a rant without much substance. But I could be wrong. Feel free to elaborate.