I suggest that you do not. It is only a option for those who are building new systems, repairs due to failures, or upgrading from a much older card. Your GTX275 should be enough for most users but I see that you have that itch like every one else so I suggest that you either go sli or something better like a GTX470.
All in all, it's considered an "upgrade" but not by much. Unless you can sell the GTX 275 for a reasonable price and also pick up a GTX460 1GB for around $200, then the upgrade should be considered. Otherwise, you're better off waiting another year before thinking about upgrades.