Not that large - most iPhone devs are poor and value there time less than money. But I think if you move away from "library" towards "I will solve your problem around X so you don't even have to think about it" there will be more people like me willing to pay. I didn't write my own analytics because I enjoy doing it - I needed the data but I didn't want to give up all my data to admob/mobclix etc to party on, and I wanted data to be high-granular.

Here is one guy selling stuff: http://www.drobnik.com/touch/ I planning to buy his calendar control because Apple can't be arsed to give me theirs and I don't want to spend weeks writing my own.