Much written on this topic already, but none so far expressed my perspective. In fact, I've heard a number of people say +3 tomes aren't a big deal and won't influence them much.
Respectfully, +3 tomes for all my toons will be huge. What it means for me is Action Points.
I will have the flexability to drop that last level of enhancement to whichever stat and still come out even.
FvS charisma III becomes charisma II. Save 6 action points. Same end bonus.
This could mean 0 -10 extra action points at the end, depending on build and gear, while ending at the same stat.
Action points are just about the only thing in the game you can't grind more of, can't enhance with a better item. In some sense they are the great equalizer, a noob having just the same AP per level as a completionist.
(Personally I tend to spread them out, preferring a lot of weak abilities instead of one maxxed out, but it does depend on build.)
Anything that gives me a few more action points to spend is a very big deal.
Note: I only have a few toons, so it's easy for me to buy supreme's on them.