I know alot of the differences between the 06 and 07 TL's were cosmetic, however, my question pertains to engine and performance modifications.

For instance, does a 06 cold air intake fit an 07? Stuff like that.

 

yes it does, also it fits the type-S's 3.5 liter engine as well. Besides the cosmetic changes, a TL type S was added supporting a 3.5 litre engine compared to the 3.2 litre engine the normal TL's have.