for those of us already on 0.8 who mine but don't tweak around with tx construction, do we need to upgrade?
No; the only 0.8 users who should upgrade are miners who are creating blocks themselves (mining pool operators, solo miners, or people using p2pool).Big merchants/services/exchanges who want to be as certain as possible they don't end up on the wrong side of a blockchain fork should also upgrade, although I think the risk of that happening if they keep running 0.8.0 is small.