When I had mine, one good option was to disable the quick menu. It makes the console in standby and seeking updates. At least when the console is being used, you can disconnect the console from the internet and see if it is a "safe update" until connecting again instead of the console being updated without you noticing.
And the other thing is that, in the later versions of the OS, the quick menu was kinda useless and clunky. The interface was already good enough to browse around instead of when it launched and many times the page wasnt properly updated to show my recent games and it doesnt show the full library, other issue is that, if you use hard drive enclosures instead of proper external hard drives, it keeps spinning even if the console was supposed to shut down. The wii u menu is only slow if you are using a bad hard drive, when I had mine the menu was very snappy because I was using a external hard drive, it was slightly slower when I had to use a flash drive for some time.