I've got a 2001 15-45x65 Diascope. I've never looked thru anything that made me want to change. Took it to Yellowstone this summer and compared it to a Leica big one; on the same power I gave up nothing. You could go a little later with the Leica but they were both still watching after dark. Lent it to a buddy for his goat hunt in Idaho so his help had some good glass. He told me it made his 62mm Leica look like a Nikon.
Only way I see changing out mine is if I win a Swarovski ATX raffle; there are a few times it would be nice to have a little more power and a bigger lens but I am VERY happy with my compromise.