Overall, I think is a great approach. [My houserule is to handle L4, L8, L12, L16, L20 stat bumps as an increase in the point buy system, so I favor this kind of resource spending.]
Because metamagic feats can be applied to many different spells, to me they would always ping as 10 (excellent) or 8 (new tactical possibilities).
Originally Posted by sonofzeal
I think the latter comment ("carries its own cost") shows you have more rules at work that aren't listed in the bullet points of the premise. It'd be good to articulate those other factors. Here are other possible factors:
The number of prerequisites a feat requires could be a factor. Use 10,8,6,4 FP as a baseline, then calculate 12-(# of prereqs), and take the lower score.
A feat could have different costs for different classes. A preparation caster with a huge spell list like a wizard, cleric or druid gets much more versatility from a metamagic feat than more limited casters like sorcerers, bards, rangers, paladins, or beguilers.