It isn't a real problem for most of us and those who venture above 6k metres factor in the loss of a tent due to UV exposure in the costs of climbing, but there are some of us who do on occasion set up our very expensive tents in bright sun for relatively long periods of time.
Because I knew of these dangers I tried to always use an extra cap-fly over my external framed tents and/or carried some extra poles and a second fly when based in one spot for more than a day or two
I don't think recent advances in fabrics and coatings have changed my mind about this practice but the extra load is now a lot lower as would be the total load-out
How many of you would take the extra 300 grams to extend the life of your chosen tent by a decade?
How many of you would take using an extra fly into consideration when looking at a new tent?
It wasn't a consideration when I bought mine, it was simply serendipitous that $8- tarps from K-Mart fitted the Plateau perfectly and I bought them when I saw them on clearance cheap