I don't think that tensioning and detensioning make any real difference. What you need to do is bring the wheels to full tension then stress relieve the spokes, etc... If you buy a factory wheel there is theoretically no real harm to them so long as the spokes are brought up to tension and stress relieved. Where the problems cro up is when that is not done, or the components are of unknown source. Matched components that play well together can be critical to touring wheel longevity.

These two factors essentially build, and component mix, are 99% of wheel longevity, while butted or not butted are likely not even 1%. The main advantage to hand built wheels is ensuring the component mix and build quality. Down the road, though, large savings can be achieved if one can only replace the rims as they wear out, as the spokes and hub life can extend to hundreds of thou miles. Even big name builders like White will not recycle your spokes which is too bad as it makes for a more reliable wheel down the road.