Thank you to all of you who have posted replies (and keep them coming if anyone has anything else to add!)--you've given me a lot to think about. Wolfie mentioned the fact that I'd have "twice as much dog" and that's something I'd thought about that I forgot to mention--much of the time I do the walking because I'm home more, and Lefty, at only 45 pounds, sometimes pulls me along. I like his size, though, so I would want another dog about the same size, and that would be 90 total pounds of dogs I'd have to walk! (I weigh 100, which I think probably doesn't help.)

Catnapper, your Nicki looks a lot like my Lefty in the face--what is she? Mine is a Greyhound/GS mix with a brindle coat and floppy ears.

I've always loved the picture of Sylvia and Harley--that's the sort of thing I fantasize about when I think of Lefty with a sister!