Can't think of a moden factory car that ran solid mounts. I'm sure there are a few? But the vast majority.......... Well you can see where this is going.
So...if the factory doesn't do something it should never be done. Ok. Got it.
Never change cam. The factory put in the most bitchin' cam ever.
Don't raise compression. The factory put CR on max kill.
Don't change displacement. The factory knew exactly what they were doing.
Tires should remain OE specified. They were the best you could get.
Never change the tune up. The factory spent trillions making the tune up just right.
Don't even think about changing converters. The factory spent trillions perfecting those too.
If you are going to change rear axle gears...only use OE available gears. Any lower and it's never been tested.
Headers? Are you outside your mind???? A dozen engineers in at least 8 fields spent trillions designing those exhaust manifolds to perform for the life of your car. To modify or change them would be idiotic at best. You can't do R&D like the factory.
New carb? Bullshit. Why change that? The factory worked like dogs sorting out exactly what you need. You'll just **** it up with a carb way to big and kill everything below 7500 RPM.
What's wrong with the factory intake manifold? Not a thing. It was designed to be manufactured easily, fit under the hood, operate from sub zero to Africa hot conditions and still pass idiotic government regs. You damn sure can't beat that.
Why would you consider porting your cylinder heads? Millions of dollars of science and testing went into developing the best port for displacement/rod ratio/effective RPM and you, as a mere amature can't possible improve on perfection. All you will do is raise the effective RPM and ruin every other part you should not touch. It's way over your head. Don't bother.
It's a serious waste of time to recurve your Chrysler distributor. Thousands of hours went into developing the timing curve that was installed by the factory. You can't possibly know more than the factory.
Using this logic, there is no reason to change anything. The FACT of the matter is plain and simple. The OEM's only need to make a part good enough to get past the warranty. To, about 5-7 years because in the 60's and 70's that's all the longer most people owned a car. Once you sold it, the warranty was gone.
And cost. Never think the bean counters don't rule the corporate world. When new, there is very little difference between the rubber and solid mounts as far as driving feel. But 5 years down the road the rubber will start to get soft and wear out. Now, we have added a part that most people pay to have changed out. This means the company that provided that mount has a guaranteed revenue source for that part well past the production life of the car. The aftermarket suppliers love that built in revenue source and may even cut the price down a bit because of most likely future gains.
And last but not least...is cost. A rubber biscuit style mount is next to dirt cheap to produce. It is literally two studs pressed into plates (only real labor is cutting the plates of the stock and installing the stud in each plate) that are then set in a mold and hot liquid rubber is blown into the mold. Once the mold cools a bit, they knock the mount out and there it is...cheap and easy and will last long enough to make everyone happy but the car owner.
Let's look at the solid mount. First you need a length of plate. Then you need a fixture to take said plate and wrap the plate around the fixture. While still in the fixture, someone or a robot must then run a bead of weld down one side of the mount. Then the two studs need to be fitted and welded into place. When all that fun is over, the part now goes out to be tumbled a bit for the correct surface finish and then gets a swim in cad plating sauce. This is more labor intensive and more costly due to finish processes by far than the rubber mounts costs.
So we see boys and girls...manufacturers almost never deliver the best. They deliver good enough for the first owner and good enough that our outsourced supplier can make his money on that part for the next 12-20 years.
The factory uses rubber mounts because they are CHEAPER to make. It isn't rocker surgery. It's simple economics. It's called Mitt Romney republicanism. Planned obsolescence. Or certain life cycle. Or many other terms meant to say that the manufacturer can skimp and make junk as long as the part can go past the projected minimum miles or time.
Rubber mounts are NOT better but they ARE cheaper. That is all.
