I would love to sell out Dolly and go to 4down, however, I like the versatility of being able to take our choice of vehicles depending on the needs of our destination. We have a 2 door Jeep we typically take with us which is fine for the 4 of us, but this May we are going to Pigeon Forge with a 5th person and the jeep is impractical, the Saturn Vue or the Ford Fusion will work though. We (the DW and I) can pretty much load the car on the dolly and have it strapped down in under 10 minutes.
As we get older and become Full-Timers or Most-of-the-Timers, we may buy a new car/small SUV and set it up 4 down so we don't break a hip getting up and down off the ground.