You could try upgrading parts? Wheels, bars, cranks etc. I'm not really sure what you're hoping to achieve. Are you looking to make the bike better? Or just feel a bit better? Try cutting down your bars a bit, increasing tyre pressure, chain tension?
I'm not sure that turning the stem upside down is a particularly good idea. It's designed to go one way, flipping it over may have implications. Why would you do that anyway? Also, what have you done to the hub?
Changing the weight could affect how it rides. Cutting bars (as mentioned), or unwanted seat post, axles, taking off the front brake.
I think when dirtjumpP.1 said new cables/pads, he meant that it can change the feel of the bike, and really improove braking performance (new lubricated cables etc). The gyro on your bike (I think it has one) sometimes reduces the brake performance. You only need it if you intend to do multible barspins. For just a couple, and regular cable, cut longer than normal would be fine.
Hope this helps