You could have pretty much just said, "Everything" in the OP and gotten my support...

Well... Except for dying and dropping your weapon as per the first incarnation... That was bad...
Or the relative lack of interest on SoA's part...
Or the team/guild bollocks from BB...

But everything else...

That said, rare enemies would only work here if they changed the loot system to not follow the standard "Only bosses matter" approach, and instead had the chance for ALL types of enemies to drop something of note.
They'd also need to improve the game's itemization so that items actually would have some reason to be notable as well though. Otherwise it'd just fall flat.
Much longer dungeons with progression of levels/stages would help as well. Preferably hot-joinable...

So yeah... Back to my original point; scrap this and give me PSO. >_>