The 372 is a spectacular watch, but the 320 is one of the most versatile watches Panerai makes. Very wearable, very useful GMT feature, in-house movement.
You will pay too big a price to sell or trade your 320 for a 372.
I think the 372 is one of the nicest Panerai has made in many years, but I think you're getting caught up in the hype. With at least 3500 production they will be available. Wait and buy it when you can afford a second watch. Even if you have to pay a premium it probably wouldn't be that much more than what you would lose in trading now, plus you'll end up with 2 watches not one