Not very practical, but you could always run around with your fuel tank on empty!

That is a savings of at least 30lbs. And it sits way up high.
Going with lighter wheels like some nice carbon ones would be the best weight take'n off the bike. A bit expensive , but rotational mass is huge! Also some tires weight less than others. Like say michelin power pure's. And that weight is at the outer limits which makes even a bigger difference. Rotating mass effects all things at speed. Turning, exceleration and braking...
And yes the exhaust is a good idea as well...
As well as putting in a light weight battery, but i don't think that would be a good idea. (sprag clutch comes to mind)
Other than those's there is not a hole lot you would be able to notice for cost and the bike be what it is. You could always go Cafe' racer with a hack saw,but i don't think that is what your goal is. And there are other bikes that would make better candidates i would think..