I would rather say that it is great that i can be easily used in non-barbarian decks. The point with this card is that it is so well designed that it fits perfectly to barbarian decks (given its ability to summon even a rare one at no cost with additional bonuses, then drawback is almost non-existing), but on the other hand it can be played in non-barbarian ones (especially building decks) with a drawback (The summoned barbarian is like a wasted hand slot).
Making this card conditional would turn it into just another boring keyword-only-card... (we don't have that much keyword-conditional cards that can be used effective for other deck types, vampire and post-change elven rogue are one of the few that comes to my mind.)
On the other hand, standstill
also raises wall and tower by almost the same amount (ok, 12 to 15, but standstill doesn't summon a barbarian and it gives 4 tower), it's rather strange that i see nothern mountains to be played more often than this card in construction decks.
Edit: So, i don't see why the wall gain should be lowered. It's only superior to standstil in barbarian or aggressive decks, in which it isn't abused, but used like it should. In my eyes, it's more a question of popularity...
[moderator DPsycho: added card link]