One down side: Carrying a passenger. Specifically carrying the passenger, my wife.
Tamara rode with me once on the old 50cc Italica scooter, and that was under emergency conditions. She had a flat tire; I rode the scooter into town in sub-40-degree weather, mounted the spare, followed her to a tire shop, then took her on in to work -- a couple of miles at 20 mile per hour speeds.
She's resolutely refused to ride on the Italica Bulldog with me, and I suspect she'll also refuse to ride pillion on a bigger bike.
So, one of my outside -- based on both my preferences, and cost -- ideas is something like the Can-Am Spyder:
Photo by Cjp24. Creative Commons Attribution-Share Alike 4.0 International license.
With three wheels, she'd no longer have to worry that the only thing between a safe ride and going ass-over-teakettle is my, and her, ability to balance well. The Spyder is pretty cool-looking, and from reading online reviews it looks like it has a top speed in excess of 110mph and can go 250 miles per tank of gas, although the mileage is only in the 35-mile-per gallon range.
Based on that gas mileage, I guess a car just makes better sense -- you don't get wet in the rain and four wheels are even more stable than three.
And I don't think I'd like riding it as much as I like riding a two-wheel vehicle.
And even the older used ones I'm seeing are well out of my likely price range.
So probably not. But I would like a vehicle that Tamara would be willing to hop on for, say, a run into town for light shopping or a meal out or whatever.
The optimal solution might be a Suzuki Burgman 650. It's a scooter that's well-designed to handle two riders, and she'd probably find it a lot less threatening in appearance. I've seen some pretty good deals on used 650cc models, which can hit 100+mph speeds, seems to usually top 50 miles per gallon of gas, and has a range of 130 miles or so per tank of gas. Probably a pretty comfy and reliable ride for long trips as well.