>Anyone know of a good way to effect repairs on a hinge whose mounting holes
>have stripped out?  (the ones in the body, not the door)

Try drilling it out with several small drills. There are two tricks here,
        1) get it started in the dead-centre of the remaining threaded-in bit, 
               the time spent here is worth it, centre punch it to start.
        2) don't break the drill or you're really done for.

I think these were countersunk screws, so you may be able to pilot the hole 
with a large diameter bit first, then drill using 1/8" and up sizes. Usually 
if all goes well you end up with loose curls of threads which you can 
pick/blast out.
        A tool called an Eze-out is available, it is a reverse thread 
tapered screw that you tighten into the partly drilled out bolt and thereby 
twist out the rusted remains. This helps if your drilling went astray, I've 
had mixed results with them. Neat drilling works well, puts a lot of heat 
right into that stubborn little bugger too, without torching the paint. Use 
ample WD-40. Use lower RPMs and vary the speed so you don't 'glaze' the 
drill hole.
         Clean up the threads with a thread tap if you can beg/buy one. A 
set of thread taps is also useful, overdrill the hole and tap the next size 
larger thread into it, when desperate. Welding requires weather seal 
removal, followed by lots of fun body work/paint to fix the scars!