Thanks for the quick replies!
I was trying to use "valuable" as a guide to "effective" which seems to hold true often. But fails in this case I guess. So it's probably a good deal to wield the waveblade and sell the blessed shortsword.
Why is a 10-20 Blessed Shortsword so much more valuable (700) than a 8-24 Waveblade (250)? Are those extra two points at the bottom of the range worth a huge amount more than an extra 4 points at the top of the range? If so, why?