I have no interest in reading crossovers with a show that has no supernatural component of its own. That's too apples and oranges for me.

Really? For me, shows where there is a supernatural aspect are too hard to believe as a crossover - because the supernatural stuff is so different. Magic at Hogwarts is different to Buffyverse magic, Supernatural vampires are different to Buffyverse vampires, and so on.

I like Doctor Who crossovers and Farscape crossovers (and probably other things with aliens) but the crossovers I like the best are procedural shows - NCIS, House, and so on. It's just... hard to find worthwhile ones.