Depends on what sort of spokes they are, you have not mentioned that.
With old dulled up zinc ones you are pretty much wasting your time doing anything other than a good degrease and wash with detergent. Rubbing with any abrasives and polishes will just wear more plating off and promote more corrosion and rust and make them look worse so you are better off to leave them as they are or if you really dont want to strip the wheel then, just clean the spokes and then paint them with some silver paint, but be warned, after spending ages masking everything off that you dont want painted, you will end up think why did i not just strip the wheel and get the spokes re-zinced or replace with new ones. If you read the labels of most metal polishes they will say not to use on zinc coated surfaces as zinc plating is only thin and you just end up rubbing it off. Its not the same as chrome or nickel.
If they are not rust pitted, you can wire wheel the spokes and send them off to a zinc plater and they will come back like new. Its not very expensive.
If you have stainless steel spokes then yeah you can polish them up as much as you like.