Posted By:
runscottBecause you can get them without paying the full associated premium. For instance, I sold a Matty portrait with Brown Hindu back for about 30% more than a common back would go for. I've seen Cy Young and other Matty's generate similar results. Less common 'semi-difficult' backs such as Sovereign and Polar Bear have almost no effect on HOF'ers.
I like your collecting style - why not pay a little extra and get the HOF'er with a scarce back.