I just did my "mid-term" upgrade on this PC, basically replacing bits that fit in the existing motherboard, and I hope to get a couple of years more at least out of it.
So I'm on about the best CPU my board can handle, AMD 965 Black 4 Core @ 3.4, and a pretty beastly NVidia 660Ti, and with 8 Gb of RAM.
I think it will be fine, but I also think its fairly usual for games to let you scale down the graphics to suit older systems so it should just be a matter of tweaking that to suit.
Massively multiplayer games are CPU hungry when they are controlling the actions of players you can see, but if we can only ever be in the same instance as maybe 20 or 30 ships then I think that'll be fine. I think the 'massive' part will be unseen player actions (market trades, etc), and that's doesn't require complicated physics and stuff, just information downloads.