You can upgrade AA segments with miles/eVIPs quite happily. an eVIP/miles upgrade can upgrade up to 3 segments which do not have to be contiguous but do have to be in the same direction. Depending on the AA sectors you have, you may be able to use one award/eVIP for both sectors

I don't know about CX, but iirc, to upgrade on BA, a ticket has to be purchased from BA or from certain agents

The number of miles needed depends on what you are trying to upgrade; if it is something like North America to Europe/Asia, then 25,000 is correct . The AA website is pretty decent at detailing mileage requirements ( https://www.aa.com/aa/i18nForward.do...anAirlines.jsp )

One area where an eVIP can beat miles is on something like NRT-JFK-LHR which would require , iirc, 1 eVIP but would require 2 * 25k awards

Dave