So these are basically the best items to get from the achievement store (along with varrock armor) and mostly everything else really doesn't do anything significant. However, I think it's kind of a waster to just have these two items be an exp boost as they lose much of their usefulness after you reach 99. This is why I like the Varrock Armor that retains its usefulness in all of smithing. So, I propose we add new effects to the cloak and gloves.
Cloak: 10% chance to steal another item from a stall
Gloves: 10% chance to give you extra Marks of Grace
This is following the format of the Varrock armor but the numbers are free to be tweaked. This will make these items more relevant than just faster leveling, and most people will probably reach 99 thieving before they buy the cloak anyway.