Remove weight. 
To get 10hp will cost nearly £1000. 
To get 210hp its either throttle bodies or forced induction so around £4000. 
They are pretty much as powerful as they can be out of the box. 
Some re-engineered inlets, a decent panel filter, decat and a remap will make it breathe a bit better and will make it 'feel' better but is it worth £1000?? Not in my opinion, no. 
I'd rather spend the money on a decent suspension set up and some proper tyres.