Well, a larger mirror provides a larger field of view. There are lots of other specs on reflecting telescopes that will determine more whether or not it is worth the price. Do you know the specific design type? Chances are it's a Schmidt Newton or a Schmidt-Cassegrain design. I do work in astrophysics, but I personally am not an expert on this (I do more theoretical considerations). However I do have some friends that do more hands-on observation work I can ask for specific details. The extra 2" provides nearly 2x the viewing area of the 6" telescope (area goes like radius^2 goes like diameter^2). I wouldn't say it's worth the extra money, but it also depends on the focal ability of the scope itself. Perhaps if you provided me with more information of the telescope, I could provide better advice. Or even better yet if you could try the scopes for yourself then the decision becomes pretty simple. If you like, email science line back and ask for me again. If you can provide me with more detailed specifications I can follow up these questions and hopefully give you better advice. However, I suspect that most of the extra cost in the 8" model goes more to the motor than to the mirror (although as mirrors get larger they get much more expensive simply due to the difficulty in manufacturing well shaped silvered surfaces of increasing size).