much will depend on the loading on the flight. If there is no operational requirement to move people forwards then there is no need to upgrade anybody. If oversold in a cabin and requirement to move people forwards the computer decides (is my understanding)
my experience whilst gold has been 1 x WT-WT+ upgrade (travelling as a couple and both moved) 1 x WT+-CW (travelling alone) and a splattering of Economy - CE moves...many many more flights with no upgrade