While older TVOS apps had a max download size of 200mb, this was never the full story. They are meant to download the rest of what they require after launching. This could be several GB for large games like RR3, Broken Age, etc. All the updated rules do is upfront this space so they are ready to go when first launching (and a bit less of a headache for developing).
On the surface it would seem like 64GB would be useful, but the reality is that there are painfully few of these large apps available. And the quantity being released has dropped to almost nothing over the last year. I don’t see the new rules turning anything around.
While the price difference is only $20, there appears to be zero benefits of going to 64GB. Notice that not a single person on this thread has actually experienced 32GB being a limitation.