Creating a thieve's guild, starting a cult, growing wizard's tower or other "keeps" is not only a great sink for the hoards of coin players haul in, but it firmly shifts the momentum of the campaign's plot into the hands of the players. Then the DM is playing and reacting almost to ~90% of what the players are interested in grown from the campaign's soil (which is what the DM is interested in). This combination, I think, makes for a more enriching campaign.
Factions, in general, are roughly the same thing.
A lot has been written on this, but what I like about Ben's take on factions and "keeps" is that he's developed a pretty light way of tracking these types of actions. Which is what you need in a game-- just good enough to make it work.