Well your not the first to have the idea. Proline has that exact same type of spring system in production for some monster trucks. I never heard of anyone using it in an 1/8 buggy though so it might work out good with the right setup.
oh well, atleast i have thought of that myself without knowing it has existed on monstertrucks.
Ey, instead of a droop, you can apply in a softer spring at the bottom for the third rate then make use of the traveling distance your shocks absorber can do.