We actually do something similar. Rather than using the bad that comes with (whichever expansion it is) we user the tower dispenser from, er, The Tower. Stack it to the limits (mega-Carc more than fills it), and then only draw tiles from one side. That way, even if you use all expansions and can plan for a certain type of tile coming up, you can never quite be sure than it will come up. And it also keeps the length of the game down somewhata full game of mega-Carc takes us about 3 hours, which is just too much really.
The main problem with both suggestions is that many Carc players think that memorising the tile distribution is precisely the strategic element of the gamethe aspect which separates the novice from the experienced expert. Personally, I think that Carc has the element of chance built in for a reason, and think that it's good enough to stand a little more.
I must admit, that's a really neat idea.
We're slowly working through Carc, with each game we play adding a new expansion to the mix. We started with Carc, then moved on to Carc and I&C, then Carc I&C T&B, and most recently adding the King and Robber Baron. However, we're conscious that each set adds to the game time, and with two kids under 3, time's the thing we always have least of! Using Carc, I&C, T&B and the King/Robber takes us around 90 min which is really our limit, so to add the other expansions that we're dying to try out means that something has to give....
Your idea of randomly filling the tower with tiles from all sets and then only using half for any one game really appeals to me! No game will ever be the same, and of course the more unusual tiles are not guaranteed to be drawn. In particular, tiles from the P&D and the Tower can be quite game changing, but using your method means these sets will always have varying degrees of impact each time you play. I like that!