For me it's a little different. My road bike is campy and my hybrid is shimano.
So It took me MONTHS to get used to the shifting/gearing of my bianchi road bike, and when I got back on the hybrid, it was a nightmare!
It's too bad, because I like the bike and it's very comfy, but I'm almost to the point after a YEAR of riding where I am really feeling comfortable with my gears and shifting. (I never quite got there on the hybrid btw) So when I go back,
it messes with me.
My new bike will have the same kind of gears as my Bianchi, with slightly different ratios.

So, bottom line, I'm probably only going to ride 1 bike. but if i had to ride two, I'd rather they had the same kinds of gears on them!