As time progresses, as we delve in to new musical styles and as new technologies hit the market, the desire to own new gear will always appeal to us while we're still in any kind of liberal mindset. For most of us, there is no one perfect bass, so we buy different basses for the qualities they excel in.
I, personally, am getting to the point where I don't really want any more electrics, save for a fretless, which I will get some day. I have a lakland 5 string and a P-bass, and they do everything that I need them to and more. The p bass nails the vintage fender tone for me, and the tighter strings on the lakland (longer scale length + through-body) cover all the sonic territory that I need. There is so much left for me to explore on these two basses that I feel like I could spend the rest of my life finding new ways to play them!
However, I do have the desire to upgrade the basses that I have. A jazz pickup in the bridge position on the fender would be nice, and i'm thinking of replacing the bartolini preamp with a sadowsky, filling the leftover pot with a tone control.
So, I guess, my point is, if your GAS is starting to make you a little queasy, try new things with what you have already.