My philosophy when I built that team was not attacking, I built my team on each being able to cover each-other as-well as use each other to each other's advantage.. If you catch my drift.. I had in mind being able to take a-lot of different types of attacks and return them with they're maximum.
EDIT: I personally wouldn't put another wall in, I would try and find a pokemon that can take special hit's as-well as play support and or attacker if need be.. (Hence my Tentacruel, he had sword's dance and waterfall at one point in time.. With toxic spikes and rapid spin)
That's just my opinion anyway.