Thanks for the feedback, guys. I took another look at Silverfast's settings, and sure enough, sharpening was enabled. After enabling (medium) USM in the Epson software, I could detect no difference in sharpness between the two packages, although the Silverfast did manage to give the slide a green cast.
So, I guess I'll muddle on a while longer with the 3170.
What I want to get to eventually replace the 3170 is a scanner that can handle 4x5s. I don't have a LF camera at the moment, but it is on my list of eventual acquisitons. So rather than having to buy yet another scanner once I've acquired a 4x5, I'd just as soon wait until I can afford one that'll handle everything from 35mm up to 4x5.
So far, among "reasonably priced" scanners, it's looking like the Epson 4990, V700 or V750, or the Canon 9900 or 9950. I've heard nice things about the V-series, but the price is difficult to justify at this point (got a kid starting college in the Fall, and we're trying to get some funds put away for that).
Best,
Michael