Well, it takes about 5 minutes to hook our toad up and probably less than 2 minutes to unhook it. Hooking/unhooking a trailer wouldn't be a lot quicker-----------and that's before dealing with loading and tying down the car on the trailer.
In 7 years of pulling a 4-down toad, we've only had to unhook it twice because of getting into a tight spot. A trailer would have been a problem (probably a bigger one) in both situations.
As for toad trade-in, just take the base plate off------miles don't accumulate on the odometer with most of today's vehicles when towing.
I didn't get in on the thread about buying a dp vs gasser, but after driving a dp once (a Monaco), I wouldn't consider trading my gasser even up for it. Mine rides adequately and noise levels are quite acceptable since adding $150 of good quality sound insulation to the doghouse.