A system is like a sports team - you don't necessarily want the best players you can get, you want the best team. As you move up your game, finding the right pieces to give you the best synergy within a system can be a challenge. Perhaps you don't have the right synergy yet at your new level?
Some of what you are experiencing is also probably nostalgia. You remember the excitement and enjoyment you had during that time and the simplicity of not wanting more - just enjoying your experience. I still hold a system dear to me that I had about five years ago and though I've moved well past it, part of me wishes I could rebuild it. Realistically though, I know if I built it I wouldn't have the same fulfillment from it that I had all those years ago.
It's always easy to look back on 'better days' and forget the negatives experienced during that same time - negatives that might have caused you to move the direction you are currently in.