I was considering a 2004 - 2006 CTS for the past few months and after doing a lot of research and spending time in a lot of different vehicles I went with something else.
It's still a typical GM interior in any regard - cheap, plain, and plastic. I was dead set on buying one until I drove a few other vehicles and realized that it wasn't the cats ass. Seats aren't supportive, but the exterior styling is awesome in my opinion.
If I were you, I would spring for the CTS-V if you want a CTS.