an easier solution would be to just paste over every reference to a stat with your +4 bonus. If you go one step further than the original suggestion, then you can also substitute +4 as the basis for saving throws, to which you would also add your proficiency bonus (if relevant). That way, the only thing ability scores would modify is skill checks, and you'd be free to overhaul skill checks entirely without fear of messing up the combat math.
That could work. Not sure about the skill/save point buy though. That didn't seem to work well in 3e, as everyone just picked a few key skills and maxed them. Not much different than the maxing ability scores. I actually kind of liked 4e's skill method of just a flat bonus.
So...
Remove ability scores.
Any non-skill and non-save reference to an ability score is now +3 (to-hit, damage, DC's, paladin aura's, ect...)
Skills and Saves are replaced with...
Base = +1/2 proficeny bonus (1 - 3)
Proficiency = +4 (5-7)
Expertise = +8 (9-11)
Jack-of-all-trades = +2 on non-proficent skills.
New Feat:
MOAR POWER:
Choose one of the following. You can take this feat more than once, but unless noted, you must choose a different option each time.
*+1 to-hit, damage, and DC's, You can take this twice.
*+2 to your base AC, upto a maximum of 20. (Not including shield, magic, or other buffs).
*+2 to paladin's aura (Prerequisite, paladin 6)
*+2 to bardic inspiration dice. (Prerequisite, bard)
*+2 to casting modifier.
*+3 to spells known or memorized.
*+3 to inititive.
(And similar for whatever else).