This is my first substantive post in a forum. I apologize if this thread is sufficiently old for this to qualify as necroposting.
... Like, just the tiles from any expansion ...
I love the mechanics of the base game. For me, the expansions are almost entirely about the tiles. I was playing a game yesterday with just the base tiles, and there was a battle for a large city early in the game. As I thought about it afterwards, I realized how different it might have been with expansion tiles, and then I remembered recently reading this thread, so I thought I would share:

For the photo, I removed everything except the key tiles, leaving the start tile in place for context. Below the playing area, I've put all of the tiles that could fill the FCCC hole: 4 tiles from
Base Game in the 1st row; 2 tiles from
Inns & Cathedrals in the 2nd row; 3 tiles from
Traders & Builders in the 3rd row.
Base: There is only one way to fill the hole, creating a single city with shared control. Yellow has a clear incentive to fill the hole, adding 3 points to their farm for the completed city, and Red might also be willing to fill the hole to recover the stranded meeples in exchange for losing only 3 points. But the excitement of battle has ended, at least for us.
I&C: Now there are two additional interesting options: Yellow can now either win the city outright, with a net point gain of 26 (winning 24-4 for the cities themselves plus 6 for the farm) or create 3 cities to gain 9 points. Either way, Red would likely be quite happy to draw one of the base game tiles and fill the hole. The game is filled with tension on each subsequent tile draw!
T&B: In this case, it is possible for Red to win the city outright, while adding only one city to Yellow's farm, for a net gain of 17 points (winning 24-4 for the cities and losing 3 for the farm). The tension will be extremely high now, especially if both expansions are used together!
Novel Mechanics: If the Large meeple from I&C had been involved in the battle, the implications of drawing the various tiles would expand that much more. And it isn't hard to imagine that the trade goods from T&B could influence a third player to fill the hole if the right combination of goods had been available in the large city.
None of this implies that the base game is "boring". As an inexperienced player of the game, I am definitely still learning how to effectively block invasions, avoid overcommitting meeples, and many other interesting tactics. And I wish I could tell you that the position shown in the photo evolved in a pitched battle of nerve and wits between two brilliant tacticians. But the truth is that we ended up "competing for the same huge city simply because it was the best thing to do at the time" (see Note below).
For the people that I usually play with, the tiles in the expansions add a lot of interest and excitement. We enjoy the mechanics of the large meeple and the trade goods, and sometimes the builder. We like the tiles from A&M and Tower, but never use any of the meeples or rule changes, and we gave away our copy of the Dragon. We also do love the bridges and sometimes the castles, but never use the bazaars.
The primary reason to avoid adding the tiles from the expansions is simply that the game just takes too long. Indeed, my wife definitely prefers Carcassonne für 2, which I recently acquired from the GeekMarket at BGG, because we can play in about 20 minutes. And the essence of the game is sufficiently present to keep me interested, too. (Full disclosure: the scenario in the photo actually happened in that game!)
For the past few months, I have been working on integrating our favorite elements from the various expansions into a small game, typically with just 48 tiles or with 60 tiles. The link to my blog about the ongoing effort is in my signature.
Thanks for an interesting post.
Bruce
Note: The quote is from an
old post by @danisthirsty, about the advantages of the River starting tiles, which were features in
@Whaleyland's amazing "Element of the Week" series. I have been consuming that series and many other posts on Carcassonne Central for the past few months and am extremely grateful for all the great insights and shared experience.