by the time you could get this, you will prolly be in your mid 20's. Sure you mahe be able to use the next set of spells, but most of your spells are still under 20, and like several people already said, there will always be some spells you will use for the entire life of your character.
I just got LDoN for christmas, so i havn't gotten a chance to learn much yet. Can an aug be removed from 1 item and added to another item? I'm guessing not. If this is the case, then chancer are, whatever your using at Lv 20ish will probably be replaced with a better piece of equiptment so you would lose the aug benifit.
I think this could be a nice way to get a little step up for 20-30ish casters for such a small cost of only 20ap.