The extra red of the '78 does look very cool, though.
I'll guess the '78 is lower production, so if you are looking to build something unusual, that might be a consideration. But if you want to re-sell at a profit, not many buyers out there long for the days they had their '78 CR125.
The '76 CR was much anticipated, so I'm sure they sold a boat load of them. It took a few months for everyone to figure out that the RM125A was that much better. Then the '77 RM125B was lots better still.
I remember going to the tracks in early '76 and the 125 races were loaded with like 90+% CR 125s. The line was all red or silver. Within months, it was like 50% RMs and YZs, and 50% CRs. By '78 the 125 line was like 80+% yellow.
FWIW, I had a '76 YZ125X (the hot version, with the air only forks. They also had a milder '76 YZ125C). My YZ-X was very peaky and the suspension sucked, but the magazines all said it was less peaky and better suspened than the CR.
Those non-powervalved old school 125s did not make good trail bikes, unless your trails were wide and smooth, lol. But they go like stink in a straight line, even though they don't slow down so good.