We've removed the floating items above QuickShop chests for now. Each item counts as an entity and contributes to lag, so we'll see how things go without them. The good news is, we've grown so much that even with limits in place on shops per player, we still have thousands!
It's likely that we'll have to switch to a new shop plugin anyway when 1.8 comes out as QuickShop hasn't been updated in over a year. We'll keep you updated.