Let me take a stab at this, since I'm likely going to pillage my now-tattered collection of old AD&D modules to help flesh out my homebrewed 5e adventures.Why bother even using 5E then if you're going to use a previous edition's adventures? Even if you didn't have to redo all the encounters from scratch and redo all the treasure, redo all the traps, redo all the DCs, basically remake absolutely everything in the adventure besides the maps, character backgrounds and descriptions, why even bother with 5E at all?
Why use 5e?
5e plays differently from 1e, for starters. New mechanics, new ways of the doing the old familiar-though-beloved things, ie killing things, taking stuff. Think of it as variations on a theme. The theme being "killing things, taking stuff", of course.
I'm planning on doing the absolute minimum of encounter re-balancing. I'm going to straight substitute 5e monsters for their 1e versions, with the exception of mob encounters, where I'll just 1/2 or 1/4 them or something. That might work. If all else fails, there's always fleeing.
1e traps are simple to convert. A lot of them are player-solved puzzles, ie there *is no* DC, just figure the damn thing out. For the ones that do require DCs, I'll pick numbers that sounds nice.
5e is less treasure-dependent so I'll just cut a lot, or substitute consumables in lieu of permanent items. And just make up my own items of questionable utility on the spot.
As for "only using the maps"... I hate drawing maps. Just having some nice --if tattered-- maps drawn by professionals is a big plus.