unless you need the cash for your upgrade, i would seriously consider holding onto said guitar. having a backup at gigs is always a good idea, you can have each of you guitars set up to different tunings if your into that sort of thing, or if you are recording, its always useful to have as many guitars as you can lay your hands on.
whenever i'm 'upgrading', i always look at what the guitar i'm thinking of selling is worth, and it usually works out that its worth more to me as a spare than i would get to sell it. perhaps this accounts for why i now own 9 of the suckers....