[Striiker]

I have never been hung up on worrying over maximizing my XP per kill when grouping. I've seen people who will refuse to group with players that have racial and hybrid experience penalties because they wanted the maximum XP possible per kill. So, Troll Shadowknights were passed on for example (by the group leader at the time).
Where possible, it's better to group with others around your level however you should not be the big limiting factor. I have always grouped with whomever was available to fill out that last slot as long as they got XP and we would get XP and also they had to be of a level sufficient for the zone we were in.
Level 54 really sucks (as you most certainly know). It takes a LOT of XP to get through it. Accept it and just play until you level up. Level 55 XP will go much faster for you. Level 59 is another horrid level. Once you hit 59, just ignore your XP bar :-)..

To answer your questions directly.. I think that many are aware of how the XP system works on this server to a limited extent. They probably understand the basics of hell levels and XP penalties. The XP system is an accurate representation of how this all worked back in 1999 / 2000.. Regarding saying no to a grouping opportunity if full of high levels.. I never did. XP was slower but at least I was grouped and having fun. Sitting around LFG pulls in far less XP and is boring..