We've done it all: flat-towed, dolly, no toad and rent-a-car. Since we have a used-car dealership, we constantly switch cars. Since most smaller cars are front-wheel drive, the dolly ($900 used) is the easiest solution. Its drawback? Ed invariably is on the ground on his back hooking up the all-important dolly-to-car safety chain. Its pros: lets us decide at the last minute which car we will bring along.
We flat-towed a couple of Wranglers. Hookup is easy (and "cleaner"); but there's still the "fiddling around" setting up the Brake Buddy, etc. Once you have the setup, switching the toad is just a matter of having new mounting brackets installed - but some brackets need to have the bumper cut for openings, etc. I did the math one year before we went to Florida for a few weeks: the small loss of MPGs by towing still was cheaper than renting a car; plus having a car available at the drop of a hat is pretty handy.
I do agree with Bobbo - maybe getting a new car now for your wife/specifically chosen to be a good toad, would be the best (cleanest) solution?