I say go for it! We either refinish or paint most of our type banks to clean them up and give the studio a cohesive look. Many printers do, and rehabbed ones will still have the same value, if not more. And honestly, type cases are a dime a dozen so you might as well do it!
I totally agree with Jen! Sometimes you find the most beautiful wood underneath all those coats of grime and paint. We have several that have turned out to be cherry and look gorgeous when refinished. I think a cohesive natural look (rather than industrial avocado green!) has better value anyway if you were to resell.