You can always do a high flow filter. Don't know if anyone makes a pipe yet, but I think @jak9922 did something custom in that Dept.
As far as cams and bore/stroker kits, anything that fits newer 500 Foreman's should fit the P500...
But at the end of the day, a 500cc SxS probably isn't the hot ticket for power-intensive applications like duneing. Might be better off to just trade it for something else.