The basic concept sounds interesting to me -- from other things you've mentioned it sounds like you're specifically thinking of an MMORPG (not all MMO games have to be role-playing!), but to me the concept sounds much more suited to a city-builder/manager type game similar to Sim City or the various "Tycoon" style games. Rather than playing the role of a single character the player could control a settlement, controlling a collection of characters with varying capabilities and trying to pursue one or more of the goals you outlined by creating a township which meets certain needs. You could then trade with, steal from, or attack neighbouring settlements, or perhaps even set up symbiotic relationships where each settlement's features and capabilities help the other to achieve individual goals.
1. Does it sound like an idea that players would buy into?
While I'm sure a more role-playing style game would also work, things like "creating a tourist industry" seem very unusual for that type of game-play, and strike me as something that could be tricky to implement in a way that will engage and entertain players.
I'm not familiar with any role-playing style MMOs that feature much of what you describe in more than a trivial 'tacked-on' sort of way, but if my suggestion of a sim/management style game interests you at all you could take a look at some of the popular Facebook games such as Farmville or Cityville, which are very much a simplified (but still reasonably complex and technically impressive) version of what I was picturing when reading through your original post.
2. Is there already something in that space? I did a little research, but most space-based MMOs I found focused on battles, hopping between planets and hostile aliens.
Oh, and don't get too caught up with your setting/world/background if you're researching for similar games -- while the space setting is a good one for this, there would be no real tangible changes needed to make exactly the same game with a "western" (i.e. cowboys and indians) style setting or I'm sure any of a great number of other settings.
Probably not the same players who tend to prefer standard MMORPG titles, but there may be a separate market for the type of game you're describing. Depending on how the idea turns out it might also appeal to fans of adventure games, sim/management style games, and even those who enjoy interactive fiction. Really, it would depend on the implementation as well as how well you were able to advertise and hook people in.
3. Are players likely to buy into an MMO which isn't very quest-based, and primarily focuses on PVE rather than PVP?
Hope that's helpful!
: Added additional paragraph about the setting.