Off the cuff 2nd plane criteria:

- Cheap to operate (0-320 or smaller), especially if my 'main' bird
had an 0-540 up front. Big engines are great for covering distance in
a hurry, but I've had many pilots look at my little 140 and lament "I
miss owning those little birds... I used to fly so much more than I do
now, but its just so much more expensive..."
- Get in and out of places my main bird cant. Self explanatory.
- Does stuff my main bird can't. Aerobatic... open cockpit, just
something different.

I guess that would be the main thing for me... My biggest fear owning
multiple planes would be having missions where both planes would be
equally suited for the task, because thats where I feel the redundency/
waste would be. If I'm going to go to the trouble and expense of
having two ships, I want to be able to cover the broadest expanse of
aviation experiences possible with those two birds.

All IMHO

(BTW, I'd suggest a Citabria, but I don't know the ins and outs of
maintaining them or Champs).