I see where you are coming from.
However, KERS has never really been a forefront of overtaking technology. Its been focused more towards being green. I do agree the limited use they have at the moment could do with being increased. 80BHP in cars with 750bhp is not much.
The issue however, with the 3 lap thing, is that the button then does become an 'overtake' button. To make it only work on 1/3 of the laps, it has to offer a significant advantage. As a rule of thumb, I would assume a KERS available 1/3 of the time would be 3x as powerfull. What you then end up with is something that is assumed to be an 'overtake' button.
A1GP ran with this, only the cars were limited to the number of button presses per race. It was called the 'overtake' or 'push to pass' button, and the end result was people pressing it sailing past in a straight line. Arguably that is a worse situation.
Its a tricky tightrope to walk. I think everyone is in agreement, we would all like to see cars arriving at corners side by side, and not have the overtaking done way before the braking point. The issue is, with the current regulations on aerodynamics of an F1 car, this 'catch and pull up alongside the guy infront' scenario is very rare without some sort of help given to the following driver. Whatever solution is provided, it needs to only counteract the loss from following a car, not give them a boost.
So for example:
Driver A is in front doing 1:30 laps, and driver B is behind doing 1:29 laps and catches driver A. However, the dirty air means driver B is now 1 second behind driver A, but his lap times are down to 1:30, or 1 second slower than what he can do in clean air.
A proper device should eliminate the disadvantage of following a car, but not give extra advantage to the following driver. Therefore in this scenario the ideal solution would be to make driver B 1 second a lap quicker. In theory that means they will be side by side, which is what we want.
The problems with DRS have come when the advantage to the following driver have exceeded the disadvantage of following, therefore giving a net benifit, which I agree, is wrong. However, this isnt always the case. In China I think it was spot on, while in places like Australia and Monaco, DRS provided to little a benifit that didn't counteract the speed lost following a car.
Now wether this little extra ooomph comes from DRS, KERS, or magic fairy dust, I don't really care, but providing a driver can demonstrate an ability to catch someone, and then maintain that speed to have the ability to attempt a pass, then we get good racing.
I would be slightly concerned that a 1 in 3 lap uber KERS boost would be worse than DRS. Especially if it could be used regardless of your proximity to another car. It could even promote the user of KERS to catch someone, but then run out and end up stuck behind someone.
I would also like to make the point that I think F1 is the wrong formula for KERS. KERS has shown great potential in improving fuel efficiancy and trning 2wd into 4wd at a push of a button (see Porsche 911 GT3 RSR Hybrid race car). Therefore I think GT and Endurance racing are much better arenas for KERS development. It is also much closer to road technology than F1.
With a massive rewright of the rules of F1, especially those around aero, I think we could eliminate, or atleast reduce the 'following a car' problem. But then this is something we have all known for years, and even though the FIA suggested it for 2013, they once again seem to have missed a trick and stuck with a high aero formula.