Just as an FYI. I string for a Satellite tournament that is held here in town each year. It is a tier 2 or 3 WTA event.
One of the girls turned in at least two racquets a day. They were Babolat AeroPureDrives, just like Nadal plays with. She asked that they be strung with Pro Hurricane Tour 17 in the mains at 68 and Babolat Excel 17 in the crosses also at 65. (Her tension request varied +/- three pounds during the tournament.)
The week I strung for her, she broke two a day. I noticed on her frames that they had been strung so many times that there was a line where the paint was worn off by the string crossing the frame at the 4 and 7 o'clock positions. I took care of her frames, but I can guarantee you that they had been treated as well by other stringers and were still holding up.
In other words, I don't think any of us have to worry about wearing a frame out by stringing it too much.