Yeah, would be nice if something could be done about that.
You may be able to scum for needed items in the beginning, when you're not having many unlocks, but once your itempool reaches a certain size scumming simply takes too long. And then there are items like Fabulous treasure who never appear in shop pools (correct me if I'm wrong, but I've NEVER seen it in any shops) and vicious rewards, which you can only obtain from beating the dungeons. Granted, most people here more or less eat vicious dungeons for breakfast, but having to play through an entire dungeon so you can just try something is annyoing .
Of course, you can locker those things, but than you have the choice of either limiting your lockerspace even more or going through an entire dungeon again everytime you try a combo using one of those items.
Anyway, endgame needs a shift from "time" to "gold".
Sidesteppers and Avatar's ideas are excellent;
I also think someone recently suggested something similar; a "vault" where every item you found can be stored, and from where you can put those items in your locker. Everytime you want to put something else in your lockers, you'd need to pay a large price for replacing it, but that way you would at least cut down on the scumming. (Not really much of a different idea, just throwing it out because I found it interesting when I read it.)