Good points so far.
Also this might be a little controversial, I hope not, but after a certain number of years the programming etc really doesn't matter. After a certain numbers of years, and everyone who has posted so far has trained for over 10 years will know how to progress and know how to train themselves. So that much really doesn't yield a great deal more.
The biggest differences will come from small changes and improvements in form and efficiency. That is the type of thing which will push you from a 400 to a 500 squat and then enjoy the resulting mass increases from that. This is where training around like minded individuals will net you gains, people who can accurately pinpoint small minor form deficiencies which will consistently hold you back.