I looked at the 2004 winners, and I saw Arcana Unearthed there. I said to myself, "the hell? Didn't I buy that, like, a million years ago? How old are these things?" But really, what it tells me is that by the time the awards are given, all the products are old enough for me to have looked into them and bought them or passed them by.
Perhaps if there were some products that I had never heard of that were really amazing...but I hardly ever find anything that really blows me away that I would be unaware of for the greater part of a year.
So, no. I've never bought any books because they won an ENnie, and I don't really anticipate doing so. I'll have already bought the ones I want by the time they win the award.