Given the price and availability of very high quality, very low stretch line, I just can't imagine going back with the wire/rope halyards. Replacing the sheaves is not a big deal.
If you're prepping the boat for offshore racing, it is not a bad idea at all to drop the rig for normal maintenance (replacing bulbs, checking the mast at the spreaders, checking the location and condition of the mast step, etc, etc, etc). The money you save in not having the wire/rope halyards spliced should cover the costs of dropping the rig.
If your current sheaves have burrs or flat spots, they should be replaced anyway.
If you find it helpful, my own experience with this is documented at the links below:
http://www.rambunctiousracing.com/sheaveissues.htmlhttp://www.rambunctiousracing.com/mastwork.html
