Here are a couple more materials for you to play with.
The first is a higher glossy car paint, which uses a modified angle of incident function which creates a more 'glossy' paint which reflects even better.

The second is a modified Glass which you can actually adjust the reflectance using the reflections tab. Using these two mats should allow you to create the render you want-- hopefully!

http://www.gadgetplugins.com/chippstuff/CW_VariableReflectGlass.mat
http://www.gadgetplugins.com/chippstuff/CW_CarPaintGlossy.mat