+1 studio time.
Tracking vital elements (or mixing) in a wicked studio will DRAMATICALLY improve what you're doing.
Also
As everyone says here, if you don't have broadband absorbers are and mixing in a non treated room with questionable monitors, nothing in the world is going to improve your mixes.
Also invest in some books like Bob Katz' Mastering Audio.
See
I just saved you 15 grand. This sort of practical advice will do more for your tracks than any gear under the sun. Besides good compressors.
