perhaps others with more experience will reply, I have used sprays rarely. The popular one, Print Guard I think, reportedly reduses damz slightly, another made by Lascaux (sp?) does less so..
Neither are something you want to be doing in a closed room.
I prefer to just take care of the prints, they are no more delicate than charcoals or some other kinds of art on paper. Cearly less robust than traditional photography prints though.
Tyler