Is there a way to force iTunes to reprocess the info for MP3s without removing them from iTunes and importing them again? Would like to keep the playcounts and such...

Try the consolidate library feature, that might work. Just keep in mind that iTunes might move and copy your files to its default directory structure if you don't already have it setup to do so. I know that you can also right-click on a file and left-click on Get Info. iTunes should reload the mp3 information. You can just click on the next button to cycle through your mp3s. This method will take awhile if you have a large library. I think that is about all you can do but someone might come along with another suggestion.

I believe doing this only reprocesses the MP3 tag info... what I need is for iTunes to reprocess the whole MP3 so that iTunes would correct the discrepancy that arises if I replace a VBR MP3 with a CBR MP3, which I think is the difference in the number of frames.