First a question...With new low profile tires - just because you have 20" rims does not mean the overall tire height or diameter is any bigger than an older style tire on 15" or 16" rims...did you check if the regular straps will work for your overall tire height?
The dolly maker will tell you that the straps are made for a certain tire size range, because you need to have enough material to install the strap. They will most probably also tell you that if you want to carry a car with bigger/taller tires, then you need to buy a longer strap set.
If you really do have bigger/taller tires than normal and this is going to be your permanent set-up, then you may prefer to buy the longer straps to make it easier to load/unload.
BTW, I use a dolly for the same reasons that you have stated - VERY GOOD POINTS on your part. It's so nice to see the 4 Down folks here telling you that you should do it their way
Kim and Steve, Mustang LCDR (Ret), '07 Damon Outlaw #1193
I have seen gross intolerance shown in support of tolerance, Samuel Coleridge
WE LOVE OUR OUTLAW RV