I'm playing a 13th level sorcerer, and I have to say I agree with most of the changes. Given a choice between all 3.0 spells or all 3.5 spells, I would prefer to play with the 3.5 versions. The fracturing of the multi-purpose spells hurt sorcerers the most, but I still think it was for the best.
To my understanding, another big reason for the changes, aside from the almighty balance, was simplicity and fun. Save or die spells can be fun for PCs, but they are no fun if they are cast on your character. It seems I remember someone from WotC explaining the Hold Person change in exactly these terms. In 3.0, if you fail the save v. Hold Person in round 1 you are out for the fight. In 3.5, you have a chance to make it back into the action.
I've never liked the all-day buffs, so I was fine with the reduced durations. I might have gone with slightly longer, as I hate having to waste too many rounds at the start of a combat just to get the right spells up and running. Perhaps a new kind of duration would be best, a sort of short-term contingency such as:
"1 hour/level, if you engage in combat during that time the duration becomes 1 minute/level, beginning on the round you enter combat."
This way, you could cast spells in anticipation of combat, and be ready for a fight, but they would not last all day and would still require multiple castings if you wanted to have them in place for a full day of adventuring.