there is a limit for the scroll, every scroll is single time use. (you already said so :p )
maybe high level scroll could a formation i n them that would increase the number of use with a recharge option.
like a basic level 1 scroll if you had the formation for recharge would become a lvl 3 scroll.
the detect life spell. only light element user can use that kind of radar ability if i remember well. and since they are rare to be able to give that kind of detection ability even in small range to a lot of user that would prevent ambush and the like. insane spell even with no firepower.