After just doing a round of bearing maintenance on AJ's car, I figured it might be fitting chime in on this one...
I think your bearing maintenance is probably going to vary based on how your track is. I am completely cleaning and re-lubing bearings as often or even more often than I change valve springs and when I do it, the bearings are just loaded with sand. Here in FL when our kids run off the track they are running through sand. I haven't met a bearing yet that likes to have sand in it. Of course if we could just get the kids to stay on the track that would help too.
As far as ceramic vs normal bearings...from what I read ceramic bearings hold up better in higher heat environments with less lubrication. I don't know if I would have put all ceramic bearings in AJ's car, but it already had them in it when we bought it. My backup set of bearings are not ceramic.
To replace or not replace...that would depend on the condition of the bearings. If you clean them out and they roll totally free without any grinding sounds or clicking, then I wouldn't replace them (however, if I didn't yet have a backup set I might buy a new set and move them to a backup set). Like a couple of the others said though, inspect them really good after hard contact because they can get damaged at that point too.