Okay, I figured out a big reason why I love (slower paced) RTSes, and only like, say RTTs (real time tactics) like Dawn of War 2 or why I don't play multiplayer Starcraft that much (and again, 3/4s of Starcraft players don't play multiplayer). This might help some RTS designers in the group.
I like that you build the economy. I like that you fight and command in combat.
But what I love about it is that you keep on unlocking new stuff as you build your base and survive so you can finally have the epic toys of superweapons and OP units, or the end game.
*That* gives me a feeling of truly earned power and at the same time captures my imagination.
It's not base building that is important, it is the clear progression from weak to strong. Base building is just the expression of that progression. Removing base building is removing the expression of progression. If one removes base building, it must be replaced with a better sort of progression.
With fast paced multiplayer like Starcraft, I can't ever build a truly epic army with cool units before getting destroyed. Either I strike hard early with a bunch of low level units (ie Marines or Zerglings) and I win, or more likely than not, I get annihilated with a bunch of low level units while I tried to get to the Battlecruisers.
While that may be fun for some, winning early, that just feels... unsatisfying to me. It feels rushed and also you don't get to experience much of the content because of early winning and losses.
With Dawn of War 2 (just talking about early campaigns), yes, I like the combat is better inherently, but you just get a squad(s). While a powerful squad, it's just the same squad(s) the whole game! You get new weapons, but nothing spectacular to write home about. Dawn of War 1 had much more toys to play with like tanks and aircraft and titans. Combat may be better, but at the expense of the sandboxy variety.
Unlocking (not just having, as unlocking is earning) powerful units and commander powers like superweapons to use against my enemies is why I love RTSes.
It is not (always) satisfying for people (me, at least) to win a match with just weak units in the early game because it didn't give me (or my enemy even) a chance to use cool stuff!
I don't know if that helped you, but I just had to put it into words.