As you well know, only difference between E50K and E75K is upgrade credits, upgrade list standing, and bonus Aeroplan points. Everything else is the same as E50K - lounge access, Z2 boarding, priority Check-in, etc. To me, the differences aren't big enough to warrant a mileage run.

Now...the difference between E50K/E75K and SE100K is significant enough that if you were debating trying to reach SE100K, I would say "go for it"; but E50K -> E75K is not worth it.

I've said this before - and will say it again - the only 2 status' worth having with AC is E50K and SE100K.