I think that is a creative solution. With some saying gas prices will go up, reducing weight - no matter how small - will help with better MPG.

Don't forget about them charging the same price for plastic as they do for metal, and the parts wearing down and breaking easier.

phenolic plastic engines would be a environmental nightmare

Will the car manufacturers still want us to pay outrages prices for "Plastic" cars. Rip off .... When is the public going to wake up at the outrages prices they are paying for cars. Here's an idea... don't advertise on every radio, television. Commercials cost billions, Cut that out and lower the price of cars..

The aluminum is recyclable those plastics are not. Stick with the aluminum or try titanium alloys. There are any number of ways to alloy metals...surely there is an alloy that is better than that plastic in weight and performance.
I think the metal powders that are compressed into objects are the best approach...that allows a wide variety of possible alloys and beyond with very little waste. Lasers melting powders are also interesting.
Who is going to buy a car with a plastic engine? Ceramic maybe...plastic? That is going to encounter resistance.
If plastic is so strong, where are the plastic screws and nails? When a plastic screw can cut through sheet steel like your clothes washer is made out of (self-tapping), I will take it back. A good ceramic could probably do that, but it might be too brittle and thus vulnerable to shock. We forget how great this stuff called metal is.
Electric is where it is all going anyway. You are working on horse buggies.

Plastic makes things lighter, but it absolutely fixes their duration of usefulness because the stuff is susceptible to temperature, vibration, & uv. I could only get behind this if the specs were downloadable to 3d printers (some day when pigs fly, the cost of 3d printers go down, and auto manufacturers decide maintenance is better than selling a new car for $20k every 10 yrs)

Na I don't like this. I'm all for imrproving materials for new areas but I think some things should just be left to metal e.g. especially when it comes to temperature and oils. How about making carbon fibre cheaper and making chassis's/car bodies from that and/or increasing spending on research into electric cars.

Plastic ?repairs,warpage,inserts pulling out,cracking,plastic tends to breaks down.I rather see some type of carbon/kevlar etc which would hold up much better If we could come up with faster ways to produce carbon parts,printing,vacuum forming etc.I've seen race cars with carbon fiber driveshafts,gearboxes,transaxles etc, The cost would have to come way down and the quality would have to improve a lot other wise its just another nightmare for consumers.

Why not use the same plastic to produce the car body panels , maybe even the chassis

The first Honda Formula 1 car in the 1960s used nylon for the gears in its transmission, and plastic inlet manifolds have been in use on production cars for years.