Unfortunately, doubling parts isn't the way to double the size of a ship. The real trick is getting the right parts... take the wings/pylons, for example. If you wanted to double the size of the top wing, you'd actually need about triple the parts just for the black surface alone (geometry!), and that doesn't factor in changing the support pieces and structure.
9500 is a compact ship, but also a very dense and heavy one, once you build it. I'll touch on it in an upcoming review, but the thing could double as a club. Modding up an existing model is something I encourage everyone to try, but I'd start with just building the regular ship and then playing around with how to expand it. Then pick up additional models, hit Bricklink, or just get creative with increasing the size.
There are lots of ways to do it, and the beauty of LEGO is that your imagination is the limiting thing. Don't like how something looks, you can always just take it apart and build it differently. You're starting down that road, and it's a very rewarding thing to do!
If the above post didn't offend you, you're probably reading it wrong.