How old? Wingmasters were not always a fancy, high end, shotgun. Always really friggin' good shotguns, but not with the fancy wood and finish they have now. However, as mentioned, an even trade isn't always about money. Even when you win.
It's not greener grass. Just different grass. You can think of your 500 as a low end 870. Well, more an entry level 870. Same thing only different, so to speak. Way more aftermarket stuff for 870's, if that matters. But an 870 isn't better than a 500. Think Chevy and Buick.