One of the balancing elEments of sorcery is the restriction on combining spell effects. If one person casts Enhance STR on themselves then someone else cannot cast Enhance DEX on them. Exactly what spells can and cannot be combined is a little vague, though. My point here, though, is that this balance should be taken into account when considering magic items. In reading the Eberron PDF, there is a Ring of Wizardry that increases INT and POW by 6 each. As a GM you should consider whether this, or any other permanent item, should be compatible with other spells.