I intend on have some items grow with the PCs as they unlock the hidden potential of the items or get more powerful when combined as part of a full set of gear of a former hero.
The way I am handling this is the following:
Using the treasure parcel system by the time one attains 2nd level, one would acquire a L2, L3, L4, and L5 item. So let's start with a +1 L2 item that has untapped potential.
Later when the treasure would allow for a +2 L7 item (L2+5), instead the character unlocks the potential of their L2 item making it a L7 and then in treasure they find a L2 item (or money equiv) keeping the balance correct. Unlocking potential could be a quest, could be dealing with a certain monster type, could be adding a rare gem to the blade, etc. Math/money wise this comes out equivalent to paying the difference in cash but style wise the GM remains in control of the items, which ones upgrade and which ones don't.
If a higher level item with similar theme is more interesting, one could get more creative than simply bumping the +X of the item to the next tier at each 5 level increment. Until more items are released by WOTC, giving a good example for this option is tough though.
Also, the way I handle things if I do not want to give out as much pure money by the parcel system is I let the PCs find an unspecified value of exotic components (or kill a rare critter and harvest for parts) and then I draw from their "wish list ideas". Then when they have a chance they can craft or get someone to craft so much worth of (Level and Lower Level) items from the parts much in the same way I could have handed out lower level items paid for out of the GP from the parcel. But this way means I have more options for explaining items the party can use rather than items they'll sell off. It is not always easy to match an item to an NPC/Monster that matches one of teh characters.
The last upgrade is the collection of items, the regalia of a former hero. Alone, each item might be simple a L2, L3, and L4 items but all together they could be a L7, L8, and L9 item. This is just a more complex juggling act with the first option on making sure when the items upgrade that lesser items or money show up to keep the balance.
I hope that made at least a little sense.
