Keep your GT, keep reading up and learning about the car/platform, do some minor modding to get used to working on it and where things are at, then later on you can either L67 swap, top swap, turbo, etc. Or pick up another one off craigslist for $1k that needs work, and make it a project, that's what I recommend, always have a vehicle at 100% so you can get to work, parts store, junkyard, whatever to work on the other one.
Either way, don't pay $10k for something so similar to what you already have. Once you learn how to work on the cars, you'll be kicking yourself when you realize how easy/cheap it would've been to just s/c your GT.