Smart enough. Even if you did max out Wobbuffet's Speed, it would still be too slow to surpise anyone with Destiny Bond (use Gardevoir for that trick).
In fact, you could argue that you don't *want* to boost up its defenses at all, all the better to cause more Counter and Mirror Coat pain. In which case, distribute effort as you see fit. Wobbuffet has only one stat that it needs as high as possible - HP.
255 HP, 255 Special Attack, +SA personality is not silly at all. Just don't put anything on Attack, to minimise Confusion damage.
It's an easy pokémon to train at any event. Only one moveset worth considering for battles:
Encore (from Wynaut)
Counter
Mirror Coat
Destiny Bond
And only one held item worth consideration (Leftovers).