If you really get a good price then you could do a trade in. But then you would miss out on the fun (or stress?) building your bike by yourself.

I wouldn't try to upgrade the bike, the old parts are hard to sell (for a good price).

Why not keep your current bike, go hunting for a good new frame and buy new parts each month to build a complete bike by yourself. And then use the 'old' bike during the winterseason.