I had a game a few weeks ago. I was trying to build a tall empire on insane difficulty, and things really didn't work out the way I wanted. Everyone was bigger than me, (I'd been planning on making tributaries of them, but couldn't) but at the same time, everyone liked me for some reason and would protect me. Normally I'm a big jerk, so needless to say I was a bit surprised by all this. I ended up with a large tech advantage, but so few planets that I could only field 100k in fleet power. Then along comes an awakened empire who's already taken out several smaller empires and who was attacking my allies, and fielding 1.6M fleetpower (my allies, although much larger than I, were nowhere near that).
So I split up my forces. I discovered early on that, due to my ascension perks and technology, my ships had faster in-system travel speeds than the AE. I would take my main fleet, run it through a system, and wait to warp out until the enemy mega fleet was over the star. Rense + repeat, and meanwhile I had smaller fleets picking off starbases and such. As the AE had dozens of planets, I was able to get enough of them that he conceded defeat.
Ten years later he declared war again. This time he's split his fleet into 4 fleets of 400k each. I tried the same tactics as before, and was still able to outpace him, although I had to be very careful because if two of their fleets went after one of mine I had to make sure they couldn't ambush mine. I got ambushed several times, but at the end of the war I'd won - albeit with very few ships left.
A third war occurred. I'd rebuilt my fleet, and started sending them out in small chunks - 3 battleships per fleet - just enough to kill a starbase without losses. He was ready. His ships were no longer slower than mine, not sure exactly how he closed the gap but I'd lost that advantage. Also he had less planets to defend and they were more closely packed. In short, I was getting nowhere fast when my save file got corrupted and I had to start a new game.
So, in short, raiding and hitting planets can work, if you have a technological advantage and the opponent's empire is large enough. It felt like I was manipulating the AI, especially the first war. I was surprised by how well the AI was able to adapt to the threat - although he clearly wouldn't change tactics mid-war.
It was a ton of micro, and even then it was hard to pull off correctly. It would have been a lot easier if planets gave more than 5 warscore. Or if I had better ways to increase my fleet speed (Maybe I should have been using cruisers instead of battleships?)