I don't think #2 should even be an option - it's just not fair. Say I spend a ton of money and time to send out to everyone, but others spend less than $5.00 and about an hours worth of time to send to only their friends - not fair, plain and simple.

I like the idea of splitting it up into dog, cat and pet, but that would be an awful lot of work for somebody to coordinate, so really, #1 is the only option.

Like others have said, if you don't have the money to send to all, just PM those who you wan to exchange with and make it a private thing. But if you're going to be part of the big list, it's all or nothing. In my opinion anyway.

Oh, and one last thought. Even though I don't spend much time on the dog side, I still enjoyed getting/sending cards to people I might not know that well. It gave me a chance to get to know them better and to maybe make a side trip over to the dog side to check their "kids" out. So my point is that even though you may not know somebody from the "other side" very well, I don't think it's a good enough reason to split the list up.