I've found that I'm perfectly happy having all of my games on my Wii U. I rarely ever sell my games, and usually when I do I regret it later.
I've listed all of my games on kijiji for $10 lower than the eShop version's price, and I'll replace the games as they are sold. And all future games I buy will be digital. I'll have to hold onto my Nintendoland disk for the time being, as it's not on the eShop at them moment.
It takes a while to download full-sized games though, about an hour and a half.
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