You've made it as a modeller when you've built everything you've ever wanted to do, to the best quality you could possibly perceive, and have therefore 'completed' the hobby, ready to start a new one... Until then, shall we all keep practicing?
Personally I'm happy to look at any of my collection and think "Yes, I've made alterations to the RTR model and changed it for the better". I think it's for this reason that my pet peeve (at the risk of going on to another topic!) is rakes of RTR stock at exhibitions. In some cases it might not take much doing, but my perception of being a decent modeller - I suppose roughly equivalent to having 'made it' - is to be competent and confident enough to change a model for the better.