Hi Mark,
I had somewhat like Bird's opinion of "plastic" for a long time, but technology has certainly changed that for the better...
As you know, I've have tractors for a couple of three days now and for some reason, units make prior to 1980 sheet metal "looks marvelous darling"... with no rust or very little...
But, I don't know what it is, at a number of auctions, most tractors after 1980 sheet metal is rusty, rustier, or just plain nasty... the average person would think they were the older units...
My Massey's are in great shape{former 1969 and going 1973}, but my Satoh {1984) has some rust... so go figure.
Now, I know you'll find this hard to believe Mark, but yes, my utility John Deere has a plastic/composite hood and metal fenders... And no the determination of plastic versus metal shouldn't be a deciding factor in purchasing any tractor...
You may feel about the plastic the way I feel about the "slip-on plastic pto covers"... somewhat humorous... perhaps not.
The major advantage of plastic over metal, I do find is mostly the elimination of "dings" on plastic that will show up and stay on metal as dents...