Does it make sense to parboil spare ribs before you roast or grill them?
I can kind of go either way on this. I like to cook my ribs low and slow with smoke, which takes a couple of hours. However, I'm not sure that par-boiling will really improve this cooking time. So I'd say no for low and slow technique. 

My mother boils her ribs first and then grills them. In this case, they cook in the liquid and really just finish on the grill. She puts the ribs in a shallow pan, puts some liquid in, covers in foil, and throws them in the oven. I think she does about two hours in the oven (a quick google suggests about 275). Then it only takes 15 mins or so to finish on the grill. This makes tending quite a lot easier. You can boil them ahead of time and hold in the refrigerator. It also allows you to introduce some more interesting liquids for the boiling (beer, Coca-Cola, Dr Pepper).

Par-boiling for 10-15 minutes and then grilling will help reduce some of the fat in the ribs. It will also help make them "fall of the bone" if you're grilling at higher heats. However, I don't think that 10 minutes is going to substantially affect your cooking time. I could be wrong though, as this method falls dead in between the two methods I'm familiar with.