If I had to choose what I believed the foundational principles of Vintage were, I'd settle on two primary ones. Firstly, Vintage is format to sling the most powerful spells from Magic's history. Secondly, a card should be restricted if it is able to either make one player an extreme favorite to win and be deployable within the first few turns of the game, or make going first a major deciding factor in each game. Coming up with one or two premises from which a sufficiently fun restricted list can be derived is difficult, and likely each card should be evaluated on a case-to-case basis. I ultimately do not believe that there should be changes to to format made unless absolutely necessary.
I think that specifically format diversity, fun and "freshness" should be factors in deciding what cards to restrict. As a format that is home to the most powerful cards in magic, the best decks will naturally either be playing these cards or be playing a strategy to minimize their impact. When the power level of a format is so high, only a few decks will naturally rise to the top. What I remember from being a kid was that Vintage was the "five pillar" format. I think that's alright. Not every deck needs to be viable in every format. It's fine that some decks that used to be the best are now marginal. It's fine that some decks aren't good enough.
Fun, as it applies to magic, is very subjective. Although you may not find playing against Shops fun, the person playing Shops may love locking people out of games. A restricted list based on what is fun and what is not would be entirely subjective.
Keeping a format "fresh" seems to be the new buzzword that's running around, but I do not think that what is in a certain sense the "historical" format needs to be as shiny as Modern or whatever. I personally enjoy slow moving formats, and would be personally disappointed if my formats became "Flavor of the Month" dominated.