We're just snobs.
Split window busses are the best. 68-71 bays are a good second choice. 73-79 suck.
There are tons of differences between early and late bay. The most major being that the engine goes from type 1 (like all of the early busses, beetles and ghias use) to a type IV pancake type with the cooling fan on the end of the crank. Some guys love those engines, and I'm not saying they are bad. But all the changes together make a 73 less desireable, more plastic, harder to work on, more expensive, just not as classic of a machine.
I'd take a 68-71 with minor rust issues before a perfect 73-79.
I see a lot of over-priced baywindows. Take your time looking. There are a lot of good ones around.