Long after you have benched Mont, Rairyuu, and Y'shtola, Vistralle will still be useful. Especially for steal heart and steal time in raids. Also, his steal skill is useful for farming mats needed in crafting. Oh, and I always bring him along for daily cactuar and gil maps.
I dunno, I use him a lot. Always save my day with steal heart and his TMR its pretty useful to add up some extra dark eater and eva (15 eva + dark eater). Good for some eva teams if you don't have all the URs maxed (Vinera, Kitone...)