I would buy a convertible with high miles. Maybe a Saab so you can fit the kids in the back on an ice cream run. You can find loads of them for $5K. Maybe a Mustang GT convertible with the big v8 and leather and such...that's America, man.
Or, a new scooter. Cept I am not allowed until kids are out of the house, because I wreck and almost die sometimes.
Another idea is a freakishly nice mountain bike. Carbon frame, weighs next to nothing.
ZTR mower and a new shed might be fun.
Put like 8 more shower heads in your master bath and get a tankless water heater.
Hot tub (might cost a few more $K, depending on options)