As I understand it the polarizers/diffusers seem to have alot to do with light output from the backlight. Such as Xenarc offering brightness enhancements by changing out the films.
As I think mentioned before in this thread, 3M makes a specific high brightness film that supposedly will increase light output by up to 165% (I'm sure you would losing a wide viewing angle however).
3M Display enhancement films
Obviously there is trade offs angle vs. light output, etc. I seem to remember someone briefly looking into this in 2001 on these boards.
As mentioned before simply switching to a higher powered inverter with the existing CCFL's will increase your brightness but obviously half the estimated life of the tubes themselves.
A combination of more efficient film, high powered inverter with dimming option and longer or extra tubes should yield a pretty impressive display.
Going by jcdillin comment about the projectors it would appear there wouldn't be a need to replace the polarizers attached to the LCD module itself to compensate for contrast ratio.
Does anyone remember off hand what the current model number is for the Panasonic module in the Xenarc?