I haven't done the shell measurements per the wiki but will when I get a chance. As far as ability and demands on the boot, my ability has actually gotten worse over the years and less demanding as a result. 10 years ago I was a very high level skier, but from that point on my annual ski days dropped significantly to the point where in the past 5 years I've skied less than I used to in half a season. That plus age (even though I'm in better shape than I was 10 years ago) and kids has resulted in me being less technically precise and less aggressive than I used to be. I still spend as much time as possible in steep chutes, walls and trees, but I don't air it out much now and don't ski at mach looney speeds anymore.
I should also clarify that what I'm experiencing isn't really looseness - my boots are still snug all around, just less than they used to be. The fit just feels a little less precise and my feet feel ever so slightly less locked in than they used to, although it's only really noticeable when I'm skiing hard or in variable snow/crud. It sounds like what you're saying, however, is that my shell fit properly to begin with, then this shouldn't have happened in only 60 or so days of skiing, in which case new liners would only be a temporary fix. If that is the case, then I might still be ok with going with new liners if they would do the trick for a couple seasons (I'll be lucky if I get in 10 days/year) IF, AND ONLY IF, I'm not going to see a big performance increase from new boots.