Blimey, I didn't mean to start another debate about whether spoke reflectors are useful or not!
FWIW my opinion is similar to several expressed already - they don't do any harm.
The wheels in question are Shimano RX31 (sub £200 disc wheelset) and they're on a steel framed, mudguard and triple chainset equipped winter bike, so I haven't any qualms about aesthetics. Thanks for the tips.