I looked on the specialized website to see the component list, and couldn’t find your bike. The only Ultegra bike I saw was a tarmac comp. The lighter the bike is to begin with, the more expensive it will be to shave weight. Any 17-pound Ultegra bike was probably $3,000 + to begin with and didn’t come with any cheap-o parts. Wheels/ tires are probably where there is most weight to lose, but it will cost you both in dollars and wheel strength. I am personally very fond of my Sette lynx saddle, which weighs <200g and costs about $30. Incidentally, I just finished my first season of racing on a bike that weighs in at just over 20 lbs and thus far the only races that I have managed to win in my local series have been the ones that included a lot of climbing. With your already light bike you will probably spend thousands of dollars just to take of a barely noticeable amount of weight. If you really have that much money burning a hole in your pocket, I know a poor cat-4 racer who could use a sponsor.