Twelve PPV's a year is a bit too much, I agree. Part of the issue is that they do typically give some extra time between Elimination Chamber and 'Mania, meaning another part of the calender needs to be crammed to compensate.
As it stands now, some of the current shows are redundant. Especially in the PG era, where the core conceit of certain PPV's can't even be capitalized on. Elimination Chamber, Hell in a Cell, Extreme Rules, TLC; all of them are based on the concept of extreme violence in at least one marque match, something that doesn't really happen anymore. You could condense them down to the most distinct of the two, Chamber and HIAC, and not really lose anything, and it would also keep the cage match/hardcore themed shows spaced out in the first and second half of the year, so there's no overload.
After that, you've got several more PPV's which don't really have any identity. Payback, Battleground. Night of Champions is getting iffy, with the midcard belts so marginal now.
A PPV schedule of Royal Rumble, Elimination Chamber, Wrestlemania, Money in the Bank, Summerslam, Night of Champions, Hell in a Cell, and Survivor Series, spaced about a month and a half apart each, would seem to cover all the bases. The gimmicks are there, the big four are there. The only problem I'd see with it (outside WWE probably having no interest in dropping PPV's, of course) is that Survivor Series and Hell in a Cell might do best to switch places and keep the Major, Minor, Major, Minor pattern going, which would move Survivor Series away from Thanksgiving.