I, too, have never shown my ticket to get into a CRC (unless, of course, I needed to check in or upgrade). Also, GM flying internationally can always use the lounge, regardless of CRC membership or class flown.

In most big airports (the kind that have lounges), it is fairly impractical to use the lounge of an airline not being flown -- they are usually in another terminal, or on the other side of the airport, etc. So I'm not sure what the big deal is anyway! If you had a two hour layover in ORD flying United, would you honestly try to use the Admiral's Club or the CRC in other terminals?