Nintendo Switch or upgrade my GPU?

Get the switch, Breath of the Wild is so much fun, Puyo Puyo Tetris, Mario Kart 8, there is a bunch of cool titles coming out for the switch. (even Stardew Valley multiplayer)
 
Depends. Are you having FrameRate drops in games or want to play at a higher detail setting? If so, go for the upgrade. But if the games you are playing are working fine, look into a Switch.