I usually tend to go for a minimum of 2 factories and a star port for planets, so this means mars is always an industrial planet for me, slowly cranking out constructors. One gripe I have is that if any planet should have terraforming potential, it is Mars! Read a science fiction novel, for heaven's sake
Anyway, yeah, I find it really isn't practical to make low quality planets research focused as this means fewer factories and 50 turns for those very costly research upgrades. Unless they have some seriously excellent bonuses. In my game now I have a c8 planet with a 100% and a 300% research tile, and it is taking it forever, even with social focus, to upgrade those research centres!
Low class planets are usually primarily industrial for me, and military focused when all the upgrades are finished, in conclusion.