If you use 360 DW brass you can have a rimmed 300 blk. Much easier to form brass, just run it through the fl sizer, no trimming. You'll have to have the breech bored for the rim and perhaps a little bit of grinding on the extractor, but the 300 blk handi-rifles can be purchased new for ~$350.
As to why one would want a 32-20 vs. a 30-30, when it comes to shooting the lighter 30 caliber bullets, i.e. 120 gr and lighter, a smaller capacity case and chamber with a shorter throat is more than likely going to make it easier to get top accuracy.