Or just make really powerful items very very rare...
The way we've handled this in my RQ3 campaign is to make the vast majority of items that one might find normal "stock" matrices and such. In that game setting at least, it should be pretty common to find bound power spirits and occasional spell matrices. Those are "useful", but not overpowered because they don't really give the players abilities beyond the norm (although they may gain spells that they might not normally gain from their cult).
Rare items are "rare". And even those are usually derived from the normal matrix creation ideology in RQ3 (and in some ways easier to define in MRQ IMO). This usually involves making temporal spells permanent. A sword with a permanent truesword is a pretty nice magic item, but again is not overpowered because truesword is afterall still a spell that a character could obtain. The power is that he doesn't have to cast this every time, and isn't limited in uses. I also created some basic guidelines for simple artifacts that essentially allow for a combination of permanent temporal spell effects and "charged" instant effects. So you might obtain an amulet with 2 uses of heal body per day (which is pretty darn powerful as well, but still utilizes spell effects that are already available in the game).
More powerful stuff, or items with more combinations of spell effects should be ultra rare and should typically require attunement in order to use. You could obviously apply limits in terms of numbers of items, but honestly unless you run a monty haul type game, you shouldn't have too much need. Our game's been running for a very very long time, and even in a top power level group, there might be 2 or 3 items that would be considered "artifacts" (and a handful of lesser items that may have special properties similar to crystals and such). We also implemented many of the Primal Order rules into our game as well (which works really well due to the point based mechanics already present in RQ).
You can make powerful item creation and use as simple or as complex as you want. I'd start out simple and rare, then see how your players react (because you don't want to turn the game into a D&D style haulfest). Then progress as you feel is appropriate.
Some example items I've tossed into my game:
Chalice of Healing: Contains two matrices for Ressurection. These can be used normally. If the chalice is filled with blood during the ritual (1 temp con loss), the chance of resurection success is increased by 30%. Anyone may use the item, but if the +30% component is used by someone who is not tied to a deity that normally grants the ressurection spell, the user is not protected from potential backlash from the underworld for his transgression. The GM may determine what consequences this might entail (it's a "bad thing"(tm)).
Mace of Dissonance: These weapons come in a variety of forms. They do normal damage for the weapon type, however when wielded, they produce an audible whiring noise. When they hit any sort of non-magical metal the rolled weapon damage is applied directly as AP damage to the item before the full damage is then applied. This means that armor points of metal armor will be destroyed before it protects the wearer. (example: A 1d6 mace hitting a person wearing chainmail. The attacker rolls 4 damage on his D6, and an additional 3 points of strength damage). First, 4 AP are removed from the location struck, leaving it with 1 AP, then the full 7 damage is applied to the location with only that 1AP subtracting). The GM may determine if other weapon enhancing magic may be cast on the weapon, but in all cases, only the natural rolled damage applies as dissonance damage.
Armor of Amin-ra: Ancient magical armor of a 1st age Yelmalio hero. It appears as an elaborate Gold collar with ornamental hanging sections in front and behind (total of 3 enc when worn). When activated, it expands and grows section by section until it covers the entire body of the (human only) wearer with elaborate gold armor of an ancient style. It takes a full round to transorm, resulting in a full suit of rune gold plate armor (with double Armor enchanting, APs need to be calculated for MRQ). The collar cannot be worn under other clothing, nor can any other armor be worn in conjuntion with this armor. The armor grants the wearer a permanent catseye when in full armor form.
Heh. Got lots of these types of things...
