I love the idea of the characters being frozen from moments in their past. I do see Dean as nostalgic and longing for the happiness he may have felt as a child - or an imagined childhood - with an idealised image of Mary. I also love the idea of Sam idealising an unknown future. Many have talked about Sam and Dean being yin and yang and perhaps that strengthens that idea (though I don't see one as being strictly "negative" or "positive" - but rather fluctuating with each other between those).
Anyway. I thought it was interesting and helped me with a new perspective on the characters.