This is an interesting thread. I have to admit: I calculate it all. I probably get close if not exactly to the gold piece on treasure values; my players are always "at level" with items by the time they level up, and they're all finding stuff that works great with their character concepts. However, the OP is right: this takes FOR-EVER. (Ironically, giving out magic items is now as much of a chore as assembling encounters was in 3.5, while the reverse was true then.)
I have also tried "wishlists" but frankly my players don't care that much and don't want to pore through all the books. My average response on a wishlist is one or two useful items, a few things that aren't that useful (because they didn't understand how it worked or forgot to check for keywords), and a good chunk of items that are 10-20 levels higher than them. Needless to say, this doesn't help much.
And sure, I've also tried a little "pick an item of level X or below" kind of stuff, but honestly that just never seems as cool as finding something without the hand-holding. Sure, you're guaranteed to get something you like that way, and min/maxers don't care, but it's still missing ...something.
I guess we'll eventually get to the point (maybe more quickly) that we reached in 3.5 where everyone just knew that there were what, 7? different items and you just got those items at gradually increasing levels. There are already some things like that (all level 3 rogues want a +1 duelists weapon, for example), but maybe we'll get to everyone soon enough. I think one of the biggest misconceptions the devs have is shown by the publishing of the 3.5 Magic Item Compendium. They expressed worry that everyone just used the same 7-ish items over and over and they thought that it was because those items were the most "maximized" or that other items weren't interesting enough. The truth is that those items were SIMPLE, and the game is already complex as it is! Adding a +2 to a number once and then forgetting about it is SO MUCH BETTER than having to constantly keep up with dozens of different items and all their powers and knowing when to use them. (I still remember a player I had once that carried a +1 shield that had an awesome - but rarely applicable - power that never actually got used because she never remembered to use it; she eventually traded it in for a +2 shield and was honestly better off.) Frankly, the daily item limit is one of the best things they came up with in 4.0, and I get the feeling they did it more for balance and less for the fact that no one can keep up with that much crap.
On the plus side, one of the most useful tools I've found so far for getting appropriate loot to people is honestly the beta version of the DDI character builder; it's nice because you can look at items sorted a) by what a character can use, b) by the type of item, and c) by item level. Sure, they don't have much in there yet, but I have high hopes for the finished product. (Plus, you can look at all the extra-broken Dragon magazine stuff!)
