I feel you CPTANT, also hate this aspect of the game, it's not very fun, it's not very rewarding or satisfying ... As Thomas once put it, it's just like vaccuming your house, a boring chores you have to do ahah.
I wish map designer would put less little rocks in their future maps. If those rocks are for decorative purpose, just use other models that contain no mass (maybe we could make alternate version of the existing rocks, where they contain no mass).
This being said, it's not much of a problem at low-medium level. As others said, just use automated reclaim (patrol, attack move) and you'll do just fine on most maps. It only becomes mandatory to use some manual reclaim when you aim for the top level, and even pros are most of the time lazy about it, manual reclaim is just something you do in the very early game.