what a statement Durango...... actually, of all the systems I designed and installed, only very, very few were for the purpose of SPL and that was only because the customer wanted it bad enough to pay me enough to make it worth my while bothering with it.
My goal on systems is not SPL at all but rather sound quality, period.

and yes, I'll agree that the only person the system has to sound good to is the owner but it comes down to what level of sound your expectations warrant.

For example, your previously mentoned placement of mids in the doors and tweeters in the upper door or pillar will sound perfectly fine to a lot of people and as I mentioned that's one of the key reasons the car companies do it that way - it's easy and sounds fine to most average customers.
others looking for a higher level of sound quality do not find that placement acceptable in the least in the vast majority of cases.

it comes down to what level of fidelity, staging, imaging, freq. response, etc you expect out of a system. that's all.
I realize that my "standards" on an audio system are going to be well above what most others on here are going to require.
Most people would find your suggestions perfectly acceptable and be pleased with the sound. Of course it would be a huge improvement over the stock systems. The only point I was attempting to make on all this is that for an audiophile those same suggestions would ruin the system.