One of my favorite blades was the original BM AFCK it had a like a 70/30 edge with the small serrated section toward the tang, it came in handy many times while workin' in the yard, it cut many pieces of wire, rope and the old six pack holders (when they were more popular).
As far as what I'd pay more for and why, the plain edge is more versatile,(sp?) to me and done correctly, (the sharpened plain edge) for it's intended job will do almost anything a serrated edge will do, even a cheap serrated knife with a decent edge will excel at it's intended purpose.
In the end I'll always pay more for a plain edge blade done well, another factor in price is probably the ease of sharpening issue, although Spyderco and diamond impregnated rods pretty much took care of that.