I use an older Epson 1640 that can do up to 4x5. It does a pretty good job but it depends on what you want to do. I only want rough web scans so don't even bother with scanning at the best settings, or any of the mucking around associated with scaning in colour, etc. (it's much slower) Of the colour scans I've printed (just a handfull), I can get pretty good 6x9" prints from 645 and slightly smaller, about 5x7, from 35mm.
Also, 'the darkroom control' is not lost in the process. Digitally enhancing images is way easier than in the darkroom. You would have to perform similar midifications if you were trying to match a wet print you've alrady made. Scanning the finished print in those circumstances might be the preffered option.