Trying it out with Naselus's Insane/Abundant mod.
This little change solves two problems at once:
1. How to limit colony spam and encourage people to build up their worlds.
2. It makes economic buildings MUCH MORE VIABLE and adds a third dimension to world building. Under current rules, the only types of worlds you should build are manufacturing or research worlds. The entire economic line is worthless. This change FORCES players to devote a certain percentage of their worlds to be "market worlds," so they can raise the money to maintain expansion.
The developers should make this change official in a patch and also adopt the changes Naselus made to the AI to account for these changes. It makes the game MORE FUN and REQUIRE MORE PLANNING. If your economy can completely crash because you over expanded, you're going to pay a lot more attention to making sure you're bringing in enough money. Under current rules the only things you should be doing in the early game is spamming out colony ships and building factories, which is sort of dumb and repetitive.