Seems to me (just like it did when I drafted him), that Guillen benefited greatly from being surrounded by better hitters in Cincy and moving to a more HR inducive ballpark probably helped that out too. Last year was his first full (or almost full year), since '98 and then he was only 22.
I was super concerned of him being a Pat Burrell this year, but now that he's starting to hit that halo lineup is just plain scary. If I were a pitcher Guillen would probably be one of the guys that I would be willing to challenge at the end of the meat of a hefty lineup. Guillen is an up and comer with lots more upside then Dye.
At the very least if the HRs don't come, which I think they will, you know he'll be a lock to get loads of RBIs and score lots of runs. If Dye stops his HR pace you can't say the same of him.