jeffseight,
I guess the big question is what is it that you think could or want to be improved? Is it bass, soundstage, dynamics? All of these will take you down different roads.
If you are happy with your equipment, then, AC cleaning, power, room treatment and speaker placement will give you more bang for your buck.
I am not a proponent of using all the same brand of cables unless your equipment is made by the same manufacturer and the same vintage. And cabling would be the last thing, but when everything else is good the cables will enhance the system.
ozzy