To elaborate....
Current Maximize provides +150% base damage (150SP) to all spells and SLAs and Empower and Intensify both provide +75% base damage (75SP) each.
Current Base Damage Profile for Fireball:
At Level 6, if you have a total of 200 Fire (+USP) Spell Power + Maximize (150) + Empower (75) added = 4.25x 39 (CL6) = 165 on non crits and no save.
At Level 36, if have a total of 1400 Fire (+USP) Spell Power + Maximize (150) + Empower (75) + Inttensify (75) added = 17x214.5 (CL33) = 3646.5 on non crits and no save.
Proposed Change to scaling SP as a % instead of a fixed amount:
At Level 6, if you have a total of 200 Fire (+USP) Spell Power + Maximize 50% boost Total Spell Power = +100, Empower 25% Spell Power = +50 added = 3.5x 39 (CL6) = 136.5 on non crits and no save.
At level 36, if you have a total of 1400 Fire (+USP) Spell Power + Maximize 50% boost to Total Spell Power = +700, Empower 25% boost = +350, +Intensify 25% Boost = +350 Spell Power = 28x214.5 (CL33) = 6006 on non crits and no save..
This about the damage increase casters would need to be relevant in DPS. And I am using a modest example for a Fire Sorc in comparisons above. I know some will be above and some below the SP example.
Heck even if you did not like the at 36 example above, you could consider elimaniting Intensify as a feat and still be ahead with one less feat tax.
At level 36, if you have a total of 1400 Fire (+USP) Spell Power + Maximize 50% boost to Total Spell Power = +700, Empower 25% boost = +350 = 24x214.5 (CL33) = 5148 on non crits and no save. I honestly would be more inclined to not take intensify for the difference in damage at least, if it was choice.