This is from the one time we tried the round 12 trading bit. There were only two human players but we got a score of 183,000. Your score of 500,000+ is awesome to see! I guess you retire in the same Luxurious estates you do if you score 125,000?
This picture is from years ago on the Atari 800 version. (2003'ish)
Honestly - we had never played the Commodore version until sometime in 2013 - but by 2013 we were down to two of us playing (other two human players either got married or moved away) and were itching for a "new" version. I have not tried this trick on the Commodore, but I can't imagine it wouldn't work.
Growing up "all things Atari" I was shocked to find out that I like the Commodore version MUCH better!
My biggest gripe is that it seems on Planetquakes EVERYTHING gets about 1/4 production... not just mining and it's certainly less than half. I think Dan Bunten moved a decimal somewhere!