I like flavor text, especially for spells. The flavor text for spells in Relics and Rituals is some of the best, IMO. You read it and you get some history of the spell, who likes to use it, as well as information about how it may look, sound etc.
If a player wants to change things for his purposes, that is great and I would encourage it. If there was nothing but a stat block many players, who would use some of the fluff description if it was provided, would just use the stat block.
Creative people will be creative whether or not someone else shows creativity before them. Less creative people may use the info to add some depth, but without it they may never bother with adding anything. Bring on the fluff, I say.