No, I'm running the whole car plastic. Alloy motor pod base probably adds more stiffness than any other part.
Stiffer car = harder to get consistent, but potentially quicker, especially on smooth, high-grip surfaces.
Foams/carpet I would definitely go all alloy. Rubber/carpet I would consider some/all alloy, well worth a test, rubber/asphalt I would also consider it but if the track is bumpy or the grip is poor you will most likely be happier with the plastic parts.
Re: shocks, I have gone for the Rayspeed RS14 piston, 3x 1.2mm holes, seems to make the car a bit more settled, less skittish, worth trying. Some people drill their own pistons, I don't trust the accuracy of my hands!
I'll just post up the stable setup, this is with a diff for maximum stability, unfortunately didn't get the chance to play with a spool at the weekend as there weren't enough blades in the "team" pitbox.
All parts/settings as Red 2007 kit unless stated otherwise.
Car: Scythe Red 2007 (plastic bulkheads/motor pod)
Front:
Pistons: Rayspeed RS14 (1.2mmx3mm)
Oil: Much More #450
Spring: TOP 1.4x5.5 (softer kit spring)
Inner camber link spacer: 2mm
Arm mount shims: 0.5mm F/R
Ride height: 5mm
Shock length: 63mm (one shock o-ring as bump stop)
Droop: 5 on gauge
Camber: 1 degree negative
Drive: Differential
Anti-roll bars: None
Rear:
Pistons: Rayspeed RS14
Oil: Much-More #400
Spring: TOP 1.4x6.0
Inner camber link spacer: 2mm
Arm mount shims: 0.5mm F/R
Ride height: 5.5mm
Shock length: 63mm (one shock o-ring as bump stop)
Droop: 4 on gauge
Camber: 1 degree negative
Drive: Differential
Anti-roll bars: None
Others:
Ballast: 55g next to ESC/motor plate (total weight 1505g)
Body: Protoform Mazdaspeed 6
Tyres: Much-More AT32 premount
Cells: IB4200
Motor: Integy Blue Atlas 19T (31/78), Yokomo S-world 9x2 (23/78)
ESC: Keyence Rapida Pro
Servo: Futaba S9550, Kawada B-29 servo saver
Radio: Futaba 3VC/R133F
If running a one-way, try an extra 1mm spacer under the front arm mounts to smooth it out, still a stable setup but harder to drive in traffic.
This should be very stable, even your granny could drive it I think!