One point of contention...

Although CLE-EWR may be a very busy route with a lot of Elites flying it, SAN-EWR via CLE may not necessarily be so. If you were to check in at SAN and be added to the waitlist for first for the CLE-EWR flight, your chances of getting the upgrade are significantly increased than if you were to ask at the gate once you've already arrived in CLE.

By getting on the waitlist in SAN, you beat all of the elites that might be checking in for that flight in Cleveland.

Regards,
RChavez