now from experience of having various cabs, I've always found once you take off the clipper kit (blue car for you) there is alot of rust underneath, thus I'm a big fan of the older cabs, as you can see where the damage is. Depending on what the underneath of the cars are like, I would go with doing up the black one and driving it as its works and get a cheap running gear for the blue one and sell it, then use the money from the Blue one to really do up the black one. Then again I would keep both and use one for day to day and one as your show car
You could always break the blue one as you will get good money for cabs in parts these days.
If you have any questions feel free to PM me.
Si