Some thoughts, to be taken with a grain of salt:
I'm not entirely sure I see the problem that your system is addressing, per se. It sounds like you're main thrust is removing existing spells for two new limited kinds of spells to make everything
always-on or
a combat one-shot with no middle ground. While I agree that buffs can add paperwork....I'm not sure how this is really alleviating that. It sounds like it's just removing the time you buff, not the actual buff.
Some of the features of the system may be attractive to players, but also sound like they're removing certain scenarios because the DM has overused them. Being ambushed and suprised is very much a classic scenario...but if buffs are running 24/7 (except for the super-short super-powerful buffs), all buffs cease to be interesting. They then become Supernatural abilities that you occasionally swap out.
How would this system interact with existing classes and spells? The sorceror is going to need rejigging, for example, as this system potentially has less to offer him than the wizard, cleric and druid. How will dispel magic effect all of these wardings and buffs and how will they interact? Unless you make changes, those wardings will still require book-keeping as some or potentially all of them get wiped out during the first or second round of combat when the initial dispels and other magic counter-measures are launched. Item interaction has been touched on, and is important. Many items will need to be changed, as well as the item creation rules. A ring of Bull's Strength becomes much more attractive than any spell-based solution as a shortie, but becomes way over-priced if it's a warding. How will abilities like the paladin's aura change? Circles of Protection? Invis sphere? These are just as much effort to track, even if you remove the timing aspect.
This all assumes that players always have ample time to rest, cast spells and prepare for any combat...which I think should happen from time to time, but it should not be the standard all the time. If a sense of urgency strikes the players as it sometimes should, moving on without a buff or holding a buff back until the right moment becomes a crucial and tense part of the adventure. Your system sounds like it means to remove that....but I don't think it will unless you change things like dispellilng. Many spells are going to be held off upon until the players are certain they need it. And with dispels flying, sometimes they MUST be cast in combat, which removes the attractiveness of your system, which sounds like mostly handwaving spell duration entirely or throwing it into the 'just for now' box.
While it is true that there are great advantages to buffing prior to combat, this is the norm at high levels BECAUSE the players have far more resources AND far less incentive to have multiple combats repeatedly. Once the group has access to things like travel magic, the tenor of battles changes. Piratecat has a story of how he planned this extensive dungeon crawl for his players, and instead the cast Earthquake and collapsed the entire complex, waited from the boss to crawl out and smacked him down. With access to magic like Scrying, Find the Path, and other high-powered divinations, players will have fewer combats as they increase in levels (instead emphasizing more sophisticated, dangerous or large-scale battles, rather than room-to-room searches).
I disagree that the cost of a spell is an action in combat. Many spells have no such cost. The cost for a spell is a SLOT. What is the cost of a contingency spell? What is the cost of a rope trick? What is the cost of a obscurring mist? A faithful hound? A Phantom Steed? Will creating two new classes of spell make things simpler or just shift the emphasis to another part of the system?
Buffs can be boring...or they can be exciting. I can tell you that my party found it pretty exciting when the wizard turned the entire combat around with a Bull's Strength on the fighter when it looked like they were outnumbered and about to be slaughtered. It turned certain death into a rout at just the right time. Now, I agree that buffing doesn't fit exactly with many stories and legends. But Gandalf also didn't cast the same spell twice, nor did Morgan le Fey create the same potion twice....but that's because those were stories and legends, not a game inspired by them. Aragorn never fought a roper...a helluva lot of orcs and goblins, but no ropers.
Now, if you're making most buffs personal, there stands the issue that you've weakend...well, just about everybody who isn't a cleric or wizard, really. The sorceror certainly isn't going to be able to capitalize on buffs with his limited selection unless he starts living off of scrolls or becomes a buffing-only guy...which would run counter to your goal. And now some buffs become useless when only personal, unless multiclassing comes into play, and even then only for a short duration. Clerics or druids may enjoy bull's strength, but wizard's won't, for example. Now you've either made potions VERY valuable, particulary to non-spellcasters (who'll be wearing bandoliers of the things) and made them far more vulnerable. Bodaks and similar creatures now should have a +4 CR, when DeathWard is no longer on the table for the melee characters, and things like poison and elemental damage becomes far more dangerous.
I'm not saying it's a bad idea, by any measure. It's actually a pretty good idea...but you need to consider the effects beyond mere buffing itself. I like the feel of the concept, but it has lots of far-reaching consequences that might not be immediately apparent. I haven't even struck out beyond the core...artificers will have a lot of heavy thinking to do.

I'm only playing devil's advocate here to spur the creative process.