Hmm, I take your point that there isn't really precedent (yet?) in 4e for complex, multi-powered items. I guess we should probably hold off on stuff like that for a while.
Hey, just got an idea how it might work after all!
I remember reading how, if you want to play a game with little to no magic items, you could do so by just subsuming the assumed bonuses into normal character advancement. That is, if you want to play without any magic items you just give the PCs +1 to attacks, damage, and defenses at levels 1-5, +2 at levels 6-10 and so on.
So how about a similar principle to magic items with multiple functions:
If you want to include a magic item that does the equivalent of two normal seperate magic items, you just make the new item that have both properties, cost the sum of their price, and occupy both their slots? (and probably uses the lower of each item's levels and enhancement).
For instance, how about if you want to have one item that does the equivalent of level 12 Bracers of Mighty Striking and level 18 Gauntlets of Destruction. You just describe it as a pair of gauntlets that extend up your upper arms, provides both benefits, occupies both slots, costs 98000 gp and is level 12.
Another example, lets say you're an orc high priest of Gruumsh and want an item that is both your main weapon and your divine focus. Introduce, the "Might of Gruumsh", a combined Terror Battleaxe +2 and Symbol of Battle +2, which consequently is a level 9 item that costs 9200 gp.
There are issues of allowing one PC to effectively hold "more items in hand than he/she should be able to" and it doesn't look to work well with armors and shields, but perhaps something can be worked out there.