Riding a car?? Riding a bike?

For most part it's easier. Because it makes you more aware of objects on roadway.  as long as you know how to drive. Awareness makes you a safer driver (pedestrians, bikes, cars...)

You still need a sense of spacial awareness, vehicle performance...(size of car, feel of brakes/gas, turning, backup...)

Smooth acceleration and breaking (feel and watching RPMs to ensure pressure on pedals) must be aware of already 1 car-length for every 10mph

Yes agree.. Car requires strong muscle memory. but Once you learn how to ride on the road then you easily handle either car or bike after little practice.

The actual mechanics of moving the car?  No.  That requires muscle memory.  However, I first took my motorcycle license, before learning to drive a car.  My instructor new instantly that I had done so, since my observations were much better.  I also positioned the car accordingly and was familiar with road signs, etc.  

When I learnt to ride, I was taught something called "Defensive Riding". This means that, rather than riding like a victim, you dominate your road space and take actions to ensure your safety, even if the pillock behind you thinks that you should get out of their way.  Although I grew up riding a push bike, that only helped so far.  Yes I rode on the roads, as well as Redways, but it did not prepare me for riding a motorcycle, since the training is more intense and you learn to be more observant and to position the bike accordingly.

If you were to use your bike for a regular commute on the roads, then maybe that would help you appreciate things like the door zone, giving other road users space and being patient.  So I think it would, without any other training, make you more patient and you may get better observations.  However, many people are not that serious about cycling and treat them as toys.  This, surprisingly, does not make them better drivers.

So I would say that, if you have had some form of training and have also spent time on the roads learning your craft, then maybe.  It is definitely the case for a motorcyclist going into a car, due to the level of training involved.  But other than that.....

Luck

It used to be assumed that a child would learn to ride a bike on the sidewalk, then ride in the street, and finally get a drivers license when they were sixteen. Of course, everything you learn about traffic from riding in the street is important to driving a car. And the mechanical skills of riding transfer to driving as well. I find that the [very few] people I know who never rode a bike are worse drivers than those who did.

In many ways you're right.  In another way, there's a glaring flaw in your theory.  If you're involved in a wreck in a car at 20 mph, you'll probably come out of it unscathed.  On a bicycle, you might be dead.  

Several links...  First of all, Bicycling Street Smarts on this link: http://www.bikexprt.com/streetsmarts/usa/  

You can take classes either in person or online from Cycling Savvy: https://cyclingsavvy.org/

Last but certainly not least, Cyclist's Eye View - parts 1 thru 3.  I'll supply part 1.  Parts 2 & 3 can easily be found on YouTube.  Nowhere in the videos will you see a cyclist hugging the curb or riding close to parked cars.  If one fool opens a car door without looking...you're either seriously injured or dead.  

https://youtu.be/ZFjCza5e1kw

There are two different features to using any vehicle in traffic:

1) knowing how to manage the vehicle as such. Steer, brake, accelerate. In the case of bicycles, how to keep it upright. How  much space you need around you.

2) knowing how to behave in traffic, the Rules of the Road. Where you’re allowed to go. When you’re allowed to go. Who’s expected to go first. How to signal your intent.  How to keep track of other road users. How to interpret their intent.

When going from riding a bicycle to driving a car, first there is the vehicle management part. 

Not much will transfer from bicycle skills to car skills there.

If you’ve ridden a bicycle in traffic, sure, that’d make you somewhat used to the environment. But as a cyclist, it’s possible to be fairly casual about the RoR without anything bad happening. 

Not so much in a car. 

Unless you’ve made a point about learning the RoR, I would not assume that bicycling ”automatically” has taught you what you need to know to drive a car in traffic.

.

Transfer skills are common. Such as (water skiing and snow skiing)(snow boarding, surfing, skate bording)(ice skating, inline skating)(para gliding, hang gliding) etc.

Yes, you have practice being aware of what the traffic around you is doing, and that carries over. Be aware though, that from inside your car you can't hear the cars around you like you can on a bicycle, so you'll need to keep checking your mirrors.