RTS idea

So, random thoughts for my theoretical uncontrolled RTS game with tons of races

in an RTS, the path to success is to quickly get your base up and running, and then to create an army, and then attack. In theory you could just keep increasing the size of your base without limit, but it's not very smart in an RTS because it's more important to produce an army and to destroy all enemies. The base is just a stepping stone to that goal. The gameplay is actually quite round based if you think about it. Round start, you create base, base creates army, army destroys enemy, round over.

But in my RTS, I want bases to be a tad more permanent, but that simply doesn't work with this design. Why wouldn't any smart faction just keep expanding larger and larger without fail? Any empty space is a treasure to be unlocked by placing buildings there!

Obviously I need to design a base system that doesn't reward such mass expansion, but I think that will be hard without making the limits feel incredibly artificial, while still maintaining the feeling of an RTS like base complex.

Possible solutions:
==Infinite Resource hubs and base upkeep==
You have to gather resources out of special places, you cannot produce them yourself. There is no point in building a base in an unfruitful spot anywhere on the map. You constantly gather resources from the hubs but your base also has an upkeep so there is a maxium size you can keep your base at with only 1 hub.
=pros=
Easy to control the growth and spread of races. Bases cannot grow forever. Motivated to attack another race to get their resource hubs.
=cons=
Finite amount of bases can be on the map. The world just became a whole lot smaller in the player's mind. The vast world isn't important, resource hubs are. Resource hubs are like the fountain of youth, nothing else in the universe truly matters. To get a reward for attacking other races you need to wipe them out utterly, thus, there are no minor victories.

==Finite resource hubs, no base upkeep, dead units leave resources==
You find rocks all about the world that have resources. After you extract their content the rocks disappear. However, when a unit dies it drops the resources used to construct them on the ground, basically making resources immortal.
=pros=
Base expansion, growth and spread is possible but it's still has reasonable limitations. Motivation to attack other races and take their resources is very high. Exploration for more materials is worthwhile, without forcing you to build more bases if you don't want to. You can attack and enemy and take resources from their dead unit without actually destroying their entire base, making long term combat more interesting.
=cons=
The player starts to view all units as walking resources. When a whole army of nasty enemies show up the first thought will be "look at all those resources!". Since resources can never disappear upgrades and research can be tricky to implement.