Pitching guro Leo Mazzone was his coach this season, and his ERA was nearly 6.00. That bodes not well.
Lopez's second half was also markedly better than his first half. You'd have to call that a positive sign heading into 07.
He's definitely a guy I'd be happy to have in the 4th/5th spot, and if somehow he reverts to the sub-4.00 ERA form, he can be that 3rd starter... though he isn't a 200 innings horse -- they'd have to manage his innings closely, I think.