I'm basically in the same boat as you, OP. My 400GB card doesn't have any space left for quite some time and I'm pretty sure 512GB wouldn't even be enough for all my dowenloaded games and DLC by now. So there is no point upgrading to it, but 1TB is just too expensive as of now. So in the end, I'm constantly debating which game to delete and many of my newly purchased digital games will simply have to wait until they get downloaded at all. For single player retail games I usually go physical, unless there is a great sale on the eShop. Multiplayer games (Smash, Mario Party and Kart) or games that are often played in short bursts (Animal Crossing, WarioWare) are mandatory downloads in my book. Indie and smaller games are usually way cheaper when bought digitally, so I don't think I have any retail version of them.
I'm also buying way too many games compared to the number of games I manage to complete at the same time. It's a habit I probably should change, lol.