I never sell any statboosters (except maybe armscrolls) since I use them for BEXP spamming. And I buy them whenever I have enough money for them, but usually I end up with not needing them.
Sometimes I wish there were buyable energy drops. For some reason, many characters with great overall stats lack strength (especially Nephenee and Marcia) >_>
As for armscrolls, it depends on my characters and how many I have. Sometimes I end up with finding one in 1-6 (I think it was there) and 2-E, sometimes I don't. And sometimes Micaiah reaches SS in Light and sometimes she doesn't. Yeah.