Good grief, no need to chuck them out. Just dunk them in hot soapy water and give them a good scrub, good as new. Don't stress about the bearings, I've done this many times over the years, as have many others, and I've never heard of any damage being done in that respect. If the accumulation of grit and dust isn't going to damage the bearing, a good scrub won't.

If you don't mind spending a bit more, you could give them a bath in some non-polar cleaning alcohol instead of water, it'll do just as well for removing crud but won't carry any risks of shorts if the fans aren't perfectly dry inside when they're next used.