I think the performance argument is bunk. Not that I put a lot of stock in benchmarks, but if performance were that much better in vanilla vs sense, I'd expect a much bigger divide. If I can hit high 1600's in a sense ROM (with all my sense widgets running) then I'd expect vanilla ROM's to score much higher. They don't. It all depends on the crap you load into the ROM, and the UI while having an affect, does not make or break performance. Optimizing any ROM will make a huge impact on performance.
You are absolutely correct about being more customizable, and the BT improvements (at least in CM).
I'm not arguing against it. It just kind of annoys me that there is this general perception that vanilla = faster/better, when this is not entirely true. If you compare stock sense vs vanilla (as close to "stock" as it can get on the DInc), then yes this applies. But this is the real world, and most people going down this path are not interested in either.