Gold Rush, I have a suggestion, keep the trike & buy a 2 wheeler to blast around town. I think I understand how you feel about getting all fixed up with some new knee & hip joints, I have had about 13 knee operations including 5 total knee replacements. It took 5 replacements, 3 left & 2 right, for me to wise up & slow down AND get a design that really fits & works for someone my size. I still have my '92 Springer for running around town and when I need to scare myself a little and I now have my '11 TG for most rides or trips. When I'm stopped, on my TG, I don't have to worry about falling when one or both of my knees decide not to work or are just tired.
So, for what it's worth, from someone that may be in a similar situation as you, keep the trike for comfort & no falling and get that 2 wheel when you need a thrill. Ride Safe