..Sure smells awfully gishy in here (Half-Orc Eldritch Knight)

[Psyren]

1) Pointless. Put in your own work for getting around DR. We've been doing it for over a DECADE now.
2) How many casters do you actually meet in combat? How many dispel at all? How many stopped when it got nerfed in PF? How many actually target weapons (which is impractical for several reasons) when they do?
3) The idea could apply to the AP enhancement, except that it ALWAYS takes the action, as opposed to >1%. You don't have to make Concentration checks out of combat.
4) You're Arcana Points could be used for better things, like all touch attacks or an actually good bonus to hit. A third level slot for an hour/level buff is pretty much a pittance when it starts mattering.

1) If it's so easy and painless to do this way, what benefit do I have doing it another way? Saving a single swift? How exorbitant.
2) My GM does use these, but then, maybe he just likes having a plausible world that challenges spellcasters and doesn't think they should sleepwalk all over everything. YMMV of course.
3) Again, this assumes the ideal scenario where your buffs remain pristine and untouched in every fight.
4) You do realize you get the AP long before you get 3rd-level slots right? And even when you do get them, is spending one of your most powerful spell slots on a mere +3 or +4 to hit that doesn't stack with what's really the best use? You could be using them on all-day flight, pounce, battlefield control, utility shapeshifting and a number of other things besides a mere enhancement bonus, and that's before we get into metamagicked lower level spells.