Edit: Ohh... For some reason I thought the full suggestion was longer than I thought...
Your suggestion is to trade the cap for abysmal free SP gain at 10% of the gain while using Boosters, which you equated to "well-rested" bonuses in other MMOs.
That boost is FAR too big, and would become P2W quickly, merely due to SP advantages those who pay wield over those who don't.
Let's give an illustration using the 10% non-rest SP -
Say the person who plays for free is "casual" and plays for 2 hours per day.
The person who, say, uses the booster half the time, is a "hardcore" and plays for 4 hours.
Then there's the uber-grinder, those who are so addicted they spend their whole wallets for a constant boost, and play 8 hours a day - as much as a job.
lets say you get 1 SP per hour normally. As that's 10% of the booster, a person using the booster gets 10 SP(!!!) per hour.
Casual - 2hrs x 1 = 2 SP
Hardcore - (2hrs x 10) + (2hrs x 1) = 22 SP
Uber - (8hrs X 10) = 80 SP

The Uber has almost quadrupled the Hardcore, and blown the Casual away with 40 times his SP!
In EVE terms, this equates to a player getting a Titan in a single month, a second person flying a Proteus at full power, while a third player can barely undock a Battlecruiser in the same time. Tell me, how is such a situation not P2W?

You have failed to draw the attention of spreadsheets online crowd (EVE) and need to do a proper spreadsheet and indicate this in the title.

WARNING: Knee-Jerk reaction of most EVE players is to rage when WoW is mentioned in reference for including a mechanic into a game... for good reason. You will encounter resistance based on that alone.

Use math to calm the raging neckbeard, and then listen and address the fact that we will find ways to break/exploit/invalidate the system.

Not because we want it to fail, but because it better be tight or it's gonna get broke fast, hard and rough. and the tears will flow when it's exploited.

Now... We kinda do have a rested SP system now, and pretty much everyone hates it. You're "rested" after server downtime.

you go from 5000-10,000 SP per match to 50

that's your 1% effect.

The neckbeards of DUST have raged because it's stupid and punishes casual play. So your idea may need a re-think.

Takes me about an hour, hour and a half, tops to hit cap. In a previous SP build it took me about 3-4 hours of bum rush and blast. You don't get much shorter than that. if the SP system goes back to the weekly cap and gives like a thousand SP per battle (just enough to keep people interested after hitting cap) then you're looking at two, three days of two hours tops each if you've not consistently hit the 600+ Warpoint per match category.

Hitting cap is easy, even if you try to be rambo. The trick is getting SP while not coming up in the red with ISK when replacing your fits. it just takes a little practice, and a willingness to deploy whatever fit you think will help win the match rather than the typical FPS stereotypical LOLPEWPEW fit over an over again regardless if that's what you need.

CCP is currently working on an SP cap that will let casual players have lives and give hardcore chumleys something to shoot for. let's see what we get before we try to re-invent the wheel.

However... If you can refine the idea further, and make it into something that fits right around the intended rate of character growth, then by all means post it. But for now, that's where we seem to be standing.

Ok... well, my original reaction was likely based upon mis-reading - And I tried not to, as the "edited" flag on my first reply marks the 3rd iteration of that post, each one based on a completely different interpretation of the OP. And it's still likely that I read it wrong that time too.
Sorry that it came off as aggressive, but I do request that you at the very least make bullet-points at the end to clarify your ideas, preventing confusion and anger in the future. Trust me on that one - I've made some pretty difficult posts.

I get the basic portion of the idea now - you're offline for awhile, and get a pick-me-up boost for a short time when you get back on, with the boost increased by length of time offline.
But we shouldn't tie the "rest" portion of SP gain to AUR, as the booster portion of the current system works just fine.
I'm thinking we can modify it as a "progressive" boost - you get the max-boost over a period, and then it starts trailing off to the minimum 10% trickle.
10% is enough of a drop to avoid hardcores getting too far ahead of the casuals, while letting them still feel like they are getting somewhere with their grinding.