One risk with doing things in isolation is hitting a local maxima. That is, getting really good using an approach that will only get you so far before super-human effort is required. For example, mastering VB 6.
It really helps when there are others who have gone ahead and made assorted mistakes to tell you when you may be following a poor path.
If you want to become better, but do not find yourself periodically challenged (or at least stretched a little), look for additional opportunities to do so.
I'm sure the Dunning-Kruger effect comes into play here.
http://rationalwiki.org/wiki/Dunning-Kruger_effect
Thinking you're great before you are, in fact, great, will surely hold you back.
I feel that I'm good but nowhere near great, I have a comfortable job in a Sydney based startup and the times where I make the biggest leaps in skill is while I'm chatting to more senior devs in our office. They always have something to talk about and give me something to strive towards.
Hope that helps, if even in the slightest.