IMHO:
" I know when I had my Mazdaspeed3 I watched people get their warranties voided left and right for the most trivial of mods." Not legally in the U.S. unless there was a direct corrolation between the mod and the failure. For example a broken aftermarket radiator hose causes the motor to overheat and blow a head gasket is direct. They can't legally refuse to warranty a wheel bearing failure based on having an aftermarket radiator hose.
"I saw guys get voided WITH ONLY THE MAZDASPEED INTAKE" Isn't that, in effect, an OEM part? Unless incorrectly installed, the dealer wouldn't have a case.
A call to Mazda should get that straightened out. If not, State Attorney General or a letter from a lawyer.
Here is an excerpt from an article I just ran across:
"There are also warranty issues related to the installation of aftermarket products and/or services on a vehicle that is still under a new car warranty. Often people install aftermarket products for adding customizing features or they use certain services for vehicle maintenance. The Magnuson Moss Warranty Act addresses such issues. This law states that if a customer installs an aftermarket product (it could be a fluid, filter, hard part, software...virtually anything that was not installed on or in the vehicle from the factory when it was new) and if the vehicle fails as a result of the installation or use of the aftermarket product/service, the carmaker cannot arbitrarily deny a warranty claim and/or void the new car warranty because of the installation or use of the aftermarket product, but must prove beyond a shadow of a doubt that the failure was indeed caused by the installation or use of the aftermarket product. The reason this law was put into place is because carmakers were arbitrarily voiding car warranties and refusing warranty service because the customer had installed an aftermarket products/services. Since there was no required burden of proof on the carmaker, consumers were hung out to dry. The Magnuson Moss Warranty Act forced the carmaker to prove that the failure was due to the aftermarket product. The law still stands today within the U.S."
John