I didn't intend to have a two dog household, but ended up with two dogs. It's definitely more than I bargained for, but it's also really great. The older dog, that was also there first, seemed to want a companion, always trying to get the cat to play and stuff. But sometimes she seems a little annoyed at Banjo's energy level, and sometimes they do fight or at this point try to fight (I've gotten good at stopping it before it starts). Banjo can be a little bratty and nasty if she has a bone to play with (but not food aggressive at all, oddly). However the majority of the time that they are active with each other, it is in play, and they both really seem to enjoy have that.
It really does have it's pros and cons. I can't say that if I had been able to make the decision myself, I would have wanted a two dog household, however now that I have it, I would never imagine not wanting one of them both for my sake, and for each other's sake.