To be or not to be.... upgraded

After speaking with the travel agency, we got a good price on an airfare to Japan. The only catch is that since they are discount tickets, they are not eligible to be upgraded, which I had intended in doing so with my excess amount of flyer miles. If I were to opt out of the discount tickets and get regular economy tickets that are upgradeable; the price of the tickets would be double. So now, I'm thinking on what I should do. The main reason why I want my seats upgraded is for my dog. Since he will be coming, having more room during the LONG 14 hour flight would benefit the dog in having more space which in turn allows me to have more leg room and there won't be as many people in business class for the dog to bother, but is it worth paying double...