I think the demo really didn't tell me much about the game... without the mods. The mods have helped me see a lot more about the game and helped me towards making a decision. There are a few bugs that are very annoying that I hope they fix. If they give this game the kind of support that I'm thinking they will from the vibe I've gotten from the Petroglyph guys and their team thus far, I think that stuff will be fixed, if it hasn't already been (since the demo is supposedly an older build).
With that in mind, I think I would probably get the full game. It reminds me a lot of Emperor: Battle for Dune, which was a great game that I also purchased back in the day. It may be worth it. I may need to buy some more RAM to get the most out of the game though... and I'm a little strapped for cash right now with having to pay for books and school supplies and such.
The big draws for me will be modability and multiplayer. Modability seems to be a given, and multiplayer we have no idea about. If it's big enough and supported enough, it could really end up being a great part of the game. If it's small and unsupported (like say, Republic Commando) then it could be one of those games that doesn't have long term appeal for me. The RAM to reduce long load times would basically be required for multiplayer, especially if you can join a game in progress...