It just depends how corroded your old spokes are, if they're not pitted they should be fine, just get 'em zinc plated mate, stay away from chroming them though, the chroming process can make them brittle, when they should be reasonably flexible to cope with the stresses induced on them. Zinc plating is also pretty inexpensive, I had all the nuts and bolts on my 350/4 re-plated for less than 50 bucks.
I suppose powdercoating would be ok, powdercoat is a plastic coating and reasonably flexible, but would add some "thickness" to the spokes, so you'd need to mask off the threads very carefully (spoke threads are very fine) and make sure the spokes thread through, and seat properly in the hub. The'd be fiddly buggers to powdercoat though, after the guys in the blasting booth finish chasing them around with the bead blaster, ha ha! Cheers, Terry.