There are a couple of tweaks which would make Explore's autocast much, much more useful.
1. Don't go back to dead-end planets or asteroids. If there was nothing there but neutral ships before, you aren't going to learn anything new.
2. Prioritize exploring (a) unexplored gravity wells (b ) closest to where the scout frigate is currently.
? ===== A ===== B ===== HW ===== C ===== ?
All scouts at A and C should scout out their respective close unexplored gravity well, instead (a) of taking 5 minutes to go back to the other one, way on the other side of your homeworld, and instead of (b ) stopping to go back and see if the neutral ships at B are still there.
If I start a game put my scouts on autoexplore and am busy queuing up more frigates / more research stations / more research / more rally points etc, it puts a serious damper on my information-gathering if my scouts suddenly decide to turn around and go through the homeworld again to look at an unexplored planet on the other side, one which would be much more easily explored by a closer scout on autoexplore.
It would also be nice if scouts later in the game wouldn't decide every so often to go on a sightseeing tour through the pirate planet, which is nothing more than a suicide mission.
Edit: Reformatted to kill the damn autosmileys.
Yes, yes, I know, "scout manually", but anyone doing their best to expand and colonize as fast as possible (in reasonably spacious maps - not in 5s) is going to have very little leftover time... (and, if the newly explored gravity well isn't a colonizable planet, you don't even get an audio warning)