Eh. Spammers only bug me in free-for-all. I'll be battling one person and then a Pikachu will use B-down for the 10928342th time and knock us both out or something. Dunno.
And yeah, it does make the fight kinda "pointless" if one person is barely trying.
If they can "nicely" spam moves, fine. Some of them are part of combos or require practice to use effectively.
Some annoying ones I can think of off the top of my head are Kirby's up-B, Ike's up-B, Sonic's neutral B, and Pit's arrows and side-B. Meh. *shrug*