There are certainly tablet games that benefit from more power.
Riptide GP2, for instance, uses a lot of water and transparency effects. It's a jetski racing game. It has a Tegra 4-optimized version and also supports the Shield controller properly.
The Mass Effect shooter looks better on a Tegra device, though I doubt it'll be updated for K1. Shadowgun or its sequels might be.
Quite a few games have nVidia Tegra-specific versions, and major publishers have been backporting Shield controller support into titles.
Games ported from consoles tend to benefit from the faster GPU as well. Much better draw distance in GTA: San Andreas, and high-res HD texture packs in The Bard's Tale.
And frankly, emulators can use every bit of oomph you can throw at them. I've got consoles up through the Dreamcast and PSP emulated on my Shield. Once you have more power than the minimum needed to run the game you can enable better filters, upscaling, and so on.
Einstein, especially, needs multiple fast CPU cores to run well. (That's an Apple Newton emulator.)
And once you get into the kind of processing power offered by the latest mobile chipsets you can start running PC software. I have DOSbox on my handheld, and have Windows 98 running in Qemu. Windows is mostly just a 'see what I can do?', but I do use DOSbox to play games. (I installed it so I could play Dungeon Keeper, because screw the mobile version.)