I should trade my P7 for Quiznos roast beef & cheddar... MmmMMm...
And if I DO decide to unload it, I'll trade it for cash (which, in this economy, is just as good as money)
I will, in turn, try and trade the cash for a Beretta 92 and a Steyer M-9A 9mm. Or perhaps a Walther P99 Compact AS. Or an H&K P2000, P2000sk, USP 9, or USP9c. Or...or...or...or...
I used to be of the "never sell or trade any gun, ever" mindset, but I've come around to "do whatever you want." If you'll use the new gun more, and be happier, go for it.
I've only ever sold 2 of mine, and it was the same situation, they were both good weapons, but I wasn't married to them. Still regretted it both times. From now on, once I own it, it stays for good.
I have bought, traded and sold guns for years. Yes, sometimes you regret a decision. There are a few I wish I have kept, but I have always enjoyed it. Plus, I would have not had all the experience I have had if I have not done it that way. I would only have limited experience with the few guns I would have been able to buy and keep. I feel, in the early years, that you learn from each purchase, trade or sell. The more guns you play with and learn about the more knowledge you gain to select your final or next purchase.