I haven't read the actual question yet, but I bet that the answer is yes.
LAN adapters are just awesome.
EDIT:
They improve connectivity a lot, I got the thing before Smash, so I dunno how much it affects that one. But online on my Wii U was literally unplayable before I got the LAN adapter, I could never finish a Mario Kart race, and Monster Hunter would get disconnected before I even started a quest. With the LAN adapter? It works like a dream, I rarely ever get disconnected, and everything works fast. Even downloading games now works just as fast as if I was downloading in my PC, which is awesome.
If you're getting connection issues, you shold definitely get the adapter.