3.P Tiered Gestalt Rules+Can I spend my CPs on ability score bonuses?

Yes.  Treat each ability score as though it were a tier 2 class.  So the first +2 bonus to a single ability score would cost 4 CP, the second +2 bonus to that score would cost 8 CP, etc. (assuming you didn't choose this as one of your primary classes).  A character with an arbitrarily high ability score and few abilities will never perform better than a tier 2 class, so eventually each +2 increase will cost 16 CP.  Permanent ability score penalties follow the same pattern, giving you bonus CP depending on the penalty you receive.

Note that these costs are delineated by ability score, so it's possible to pay 16 CP for a +2 bonus to your highest ability score and 4 CP for a +2 bonus to your lowest ability score.  These costs don't just apply to players who choose to increase their ability scores directly, but to all permanent ability score increases a character may receive outside of the standard progression (so excluding standard racial bonuses, leveling increases, or age/size changes, mythic bonuses, etc.). 

For example, both Dragons and Dragon Disciples gain permanent bonuses to their ability scores as they advance.  These increases must be paid with CP beyond the costs associated with their hit die or class levels.  Ability score increases from different sources compound, so if you take a template that gives a +2 bonus to an ability score, and then a second that gives a +2 bonus to that same ability score, you'd pay 4+5=9 CP not 4+4=8 CP. 

When taking a class, template, or unusual race, you can't forgo ability score bonuses to reduce the CP cost.  As with any other option, you must pay all CP costs to advance.  For the purposes of what qualifies as a permanent ability score adjustment, my rule of thumb is whether the bonus would persist for 24 hours in an antimagic field.  If the answer is yes, then you'll need to pay CP for it.  If the answer is no (because it comes from a spell or magic item), then you don't need to pay CP.  And to reiterate, bonuses received as part of every character's standard progression don't count toward these costs, so ability point buy, standard racial bonuses, leveling increases, age changes, size changes, or even mythic path bonuses do not incur any additional costs.  Items or abilities intended to replace items (such as Vow of Poverty) do not cost additional CP either.  Players are advised to track bonuses paid via CP separately.

2023 Note: Changes to the tier pricing have had a side-effect on ability score pricing.  Ability scores now use a unique pricing calculation.  The first increase to an ability score costs 4 CP, the next 5 CP, and each subsequent increase to the same ability score costs 1 additional CP.  So +6 to an abilty score would cost 4+5+6=15 CP.  This makes ability score increases equal to their costs in the Race Point system.  Otherwise the rules remain the same.  Penalties to ability scores can result in CP refunds, but only at half the normal rate.  So your first -2 would only give you 2 CP, for example.