Yesterday, during the writing of this random table, an idea came to my mind: how about - in some situations - introducing the items / effects that require failed saving throw to succeed? Example:
Golden Figurine of Saint Ormal: if rubbed (works once per year), save vs. magic or gain 1d8x1000 XP
It's really simple (and somewhat nasty) method of keeping PCs unsure of effects of many unidentified magical potions / dusts / devices - even with successful save player will never be sure if the effect he / she just avoided was negative or positive.
Of course, using save vs. positive effects in all situations (eg. while gulping healing potions or reading magical scrolls) would be not very good idea (unless you are really vile referee :D) but I think that from time to time it may add some spice to the game.