One of the biggest lessons I learned is to focus more on optimizing what you have before buying new stuff looking for improvements. Unless you have garbage to start with, optimization will get you more for less and make you feel like you upgraded. A 75 dollar measurement mic made as big a difference for me as when I went from sealed 12s to ported 15" subs. It's more work, can be frustrating until you get your arms around it, but can net you some real audible improvements.