Fungible Loot
I’ve been wondering lately why loot in RPGs tends to be so fungible; that is, any +1 sword is in all regards identical to another +1 sword, and every Shield of the Holy is the same as every other Shield of the Holy. Wouldn’t it be nice if there were a host of equipment properties each worth a point value, and items had a combination of properties that added up to a given point total? This is more or less how items are constructed in D&D, and I don’t see any good reason why it couldn’t be implemented in RPGs.
Examples: A sword with +1 to attack, +2 to damage, that rarely procs a fiery burst might be worth 5 points. Another sword that does ice damage instead of normal slicing damage, with +3 to damage, might also be worth 5 points (assuming damage mitigation by type is one of the game’s mechanics of course, and that slicing is more common than ice). Yet another sword might have +5 to attack, and be worth 5 points. Yet another sword might sometimes heal its wielder by 25% of the damage dealt, and be worth 5 points. So a given encounter difficulty might be assigned a loot table like “drop 2 items worth 5 points or one worth 8”, or even have a small range, e.g. plus or minus one point for each item.
Et le voila! Items are no longer fungible, and my magic sword isn’t the same as yours. Such a simple concept, and so easy to implement. Yes, there are possible mechanical consequences, e.g. players are free to build equipment collections to heighten only their attack skills, so they almost never miss, but honestly, this is far from insurmountable as a design problem.
Obviously, the larger the table of properties, the better, strictly from a uniqueness POV.
Granted, this idea is already implemented to a very minor extent in a handful of games (in that items with the same name sometimes exist, with the same properties but very slightly altered values, e.g. +4 to attack vs +5 to attack), but in general, loot tables remain filled with static items with very minor variations between them. People work to obtain the best static item they can (which they look up online of course), by killing known droppers of the item, again and again and again until they get the random drop. How tedious! With dynamic loot tables this predictability is out the window; all one can determine beforehand is that a given difficulty challenge has a chance of dropping loot within a certain point range – what’s actually dropped though will be a surprise every time.
Fool's Age 
I’d rather have the ability to customize my weapon, actually. Randomized loot drops built on a point system would be interesting… but I’d rather have control. Combine the two, though, and I’m sold. Randomize drops within a point range, and let me dissect them and reassemble them into a tailor made bonus type. That way, I don’t have to pray to the luck gods (and kill way too many things looking for just the right random drop) to get the Sword of Uberness I’m looking for, I can just build my own.
A system with tables of possible properties ties in nicely to a crafting-heavy game obviously. Depending on design goals, you can encourage or discourage people from altering or creating customized gear; I’d lean heavily towards encouraging such, as this places more emphasis on the value of crafted gear. It might take you a long time and a lot of drops to find the item that’s precisely perfect for your build, but you can keep trying and selling the failures and near-misses… or you can craft it yourself/pay another crafter.
I think it makes more sense to allow items to be broken down into components then reassembled than to allow direct alteration though, insofar as this creates a nice money and item sink to keep the economy under control. Or perhaps alteration is possible but has increased cost relative to the component cost of creation (i.e. it’s cheaper per attribute and bonus point to build it from scratch, but it might be cheaper to change a +3 attack to a +4 attack than to build a new +4 attack weapon)? Food for thought.
That’s sort of what I was getting at; that +1 Sword of Iciness would break into a metal and an Ice Rune, perhaps. Crafting would be necessary to rejigger it to where you want it. And yes, it would be a nice item/money sink.