First-year users will only vote on what they see, and if they don't consistently use the classic view - which I expect very few would - then they will most likely only vote on what everyone else has voted on. Thus, classic wouldn't be expected to be significantly different from the regular home page, and thus it cannot measure any decline.
That's not true unless those users are somehow compelled to upvote a constant number of stories, which they're not. I upvote a smaller proportion of stories on the frontpage than I used to.
I almost never vote on anything that's not already on the front page; mind you, I seldom vote up more than two or three stories per day.
Assuming that the number of first-year users' votes is noise compared to votes from newer users, and that first-year users vote mostly on items on the front page, then looking their votes alone should just give a different sort order to that front page. That's my intuition, without taking into account ranking algorithms using quadratic decay etc., but I'm not sure there's a good reason to think that would change things.
I'm not sure how accurate your assumption that new users are voters on the homepage is.
As a new user, most of my votes are on the "New" section rather than the homepage. I vote up the things that I think other people should (on New), rather than what everyone is going to see anyways because its up on the front page.
I do think that some sort of weight system for upvotes would be an interesting feature.
You're actually helping to make his point. You're a new user; you help determine what hits the front page by voting in the "New" section.
barrkel is extrapolating his own behavior as an older member: he tends to only consider front page items for upvotes.
Thus, new users determine what makes the front page, all users help determine the front page ordering, and "classic" view reflects how old users would order the front page.
The question is whether barrkel's voting patterns are an appropriate model for older members. Personally (as another older member), I visit "New" perhaps once a week, but when I do I'm much more likely to vote up a story that I find to have even a little bit of value. I only vote up front page stories that I find extraordinarily useful or interesting.
There is no reason to assume that the interaction model used by barrkel and me are representative of all older members, so while his argument is interesting, it's not very well supported.
Actually, there is evidence to support my model: the fact that classic front page is very similar to the normal front page, except with a different sorting order.
This evidence can be interpreted in (at least) two ways, (a) that most voting occurs based on the front page, or (b) that the front page topic themes, and by extrapolation user tastes, have remained consistent over time.
I (based on my own voting, and now yours too, but also the number of votes front-page articles get vs stuff that doesn't make it to the front page, evident from resubmission successes etc.) would guess that hypothesis (a) is more likely than hypothesis (b); but in any case, the fact that there's an alternative explanation for the similarity in the two front pages means that PG's hypothesis of (b) is on shaky ground.
I'll repeat (the gist of) my comment in a less crowded context (http://news.ycombinator.com/item?id=2157384):
First-year users will only vote on what they see, and if they don't consistently use the classic view - which I expect very few would - then they will most likely only vote on what everyone else has voted on. Thus, classic wouldn't be expected to be significantly different from the regular home page, and thus it cannot measure any decline.