I wouldn't call it a shoe string budget, it was worked in secret before upper management got wind of what was cooking.For a company the size of Mazda, I would consider it a hefty sum. It's true components of the chassis and it's design are shared with the Miata, but I wouldn't go so far as to call it the same platform, hence why the chassis designations aren't the same.. The FM platform is used on the Z, G, M, and FX vehicles. Vastly different in size to a 2500lbs Miata. Nissan is only on it's 2nd generation with the platform, it really isn't that old and would most likely prefer to have it play host to another generation of vehicles. Every vehicle using the FM platform has received very positive feedback with regards to the bones.
The VQ designation is a bit long in the tooth, but the engines now only share very basic design elements with the original VQ engines. They have evolved at least once every model generation. Nissan is going to tap that thing out until it's just not competitive. It is the highest performing NA V6 on the market. Even amongst all these brand new engines, it stands above the rest in terms of performance. NVH, different matter
Back the RX-8 (I really like the 09-11 redesign and came close to purchasing one). Torque is the real determining factor to when things break. Torque is the amount of force that is applied, not the actual speed of the movement (that's hp). I admit not knowing the full picture with the RX-8 drivetrain, but it really was designed around the characteristics of the Renesis engine. Take a look at how light and small components for Formula cars are! They don't make a lot of torque, but they make a lot of hp. Mazda will only overbuild it to a point, just like every other manufacturer. I don't think anyone would prefer a structurally weaker drivetrain as a cost for weight savings. That really handicaps the aftermarket community.
And BTW, thank you for keeping it clean. Even if we disagree on things, I think it's irritating when someone gets butt hurt when someone else challenges their view.