Originally Posted by Glimbur
Suppose a hypothetical human wizard. He takes 20 levels in wizard, which you wouldn't expect due to his Int and PrC's being better, but that's a different discussion. Wizard 20. Starts with 18 Int. Stat increase at 4, 8, 12, 16, 20. Int is now 23. Under the normal system, he can also read a book of +5 Int and get 28 Int. He can also age to middle aged or old if he really wants more Int. Under your system, he is stuck at 23 base int. The difference between 23 Int and 28 Int is a few plusses in skills you can already do easily by level 20, and a 3rd, 4th, and 5th level spell per day. Add in the +6 item we would expect and we are comparing 29 to 34 Int. This is an extra 6th, 7th, and 8th level spell per day. Significant? Somewhat. Is it worth making a new rule over? I disagree with you here: I don't think it is. Inherent bonuses help high level PCs be more distinct from lower level ones. Even the humble fighter appreciates another +2-3 to hit and +2-4 damage which he could get from a Manual of Gainful Exercise.
I don't think Yitzi is worried about the extra 6th, 7th, and 8th level spells per day. I think he's more concerned about the +3 bonus to all save DCs (+4 if you include old-venerable age, +5 if you're a race that has a +2 bonus to Intelligence)
With DCs, every single point counts, because it's a potential 5% increase in every one
of your offensive spells succeeding. That +5 there...that's a 25% increased success rate. That's incredibly significant, much more so than a +7 bonus to damage with a two-handed weapon (Though that itself is also pretty significant considering it applies to every attack roll)
Plus, you have to consider epic levels. Epic spellcasting focuses on Spellcraft checks. Every point of Intelligence increases the threshold for more and more powerful spells you can create and cast. (That +5 bonus? That's 5 more points I could spend creating a spell and still take 10 on my Spellcraft checks to cast it)