Enhancements for weapons and armour that add a flat cost rather than a +1 equivalent would add a lot of variety and customization possibilities to items. I would also greatly appreciate the ability for characters to customize their weapons, something more personalized than "Weapons of Legacy" and allowing characters to stick to one weapon throughout their careers.
Another thing I would like to see is weapons like some of those in the later 3.5 books, that counted as a common weapon for purposes of feats, but had a special bonus that could be unlocked by having an Exotic Weapon Proficiency feat for them.
There are also a few wording choices from the core books that could be changed, such as how shields can only be wielded in an off hand by RAW.
I also agree with what everyone else has said so far, especially about cheaper magic items and the need for a refined crafting system, especially for such things as alchemical items where multiple items can be created with each use of the skill.
