If you're interested in Eidolon, getting Eidolon and Sel-Kai City is a must. Sel-Kai is *the* city of the western hemisphere. The only problem with what you said in your first post is that it is in Emer, not Jaiman. But it's fairly easy to get there from Lethys by ship (much longer, but much cheaper, trip than with a skyship). Actually, following a trail from Lethys to Sel-Kai with stops in Norek and Artha is probably an interesting sea journey (with the risk of pirates both around Plasidar and Praeten).
Ancient ruins are everywhere. Shadow World is basically a post-apocalyptic fantasy setting several times over. You have interesting places to visit in all Shadow World products, but Cloudlords of Tanara has Merisia, the HQ of the Cult of Ezran, the Tomb of the Implementor. Vog Mur also has a bunch of interesting places waiting to be explored, but Vog Mur really is off the beaten path.
Getting involved with Iylari is probably easier if the players are in Sel-Kai (because several Namari Houses have a presence there), but meeting some even as far as Haalkitaine is possible - after all, Haalkitaine *is* the Rhakhaan capital. Once again, the idea of a trip from Rhakhaan to Emer can be threaded into the plot. You can certainly get Dyari as opponents anywhere, but I personally like to turn tables and have them as party enablers (not all Dyari are sworn to the Unlife, thankfully), and their sinister racial reputation makes them difficult to trust, which is even better (would you trust a Dyar ?). Sel-Kai has a number of *very* interesting elven NPCs (and some of my players still shudder when I mention Ormool
).
Loremasters are everywhere. Once again, common folk often distrust them or give them a reputation of troublemakers and meddlers (not entirely without reason...), so associating with a Loremaster is definitely a double-edged sword. I personally would keep Navigators at arm's length - more part of the scenery than part of the plot. Dragonlords, on the other hand... there's a reason why five of them appeared in my campaigns at one point or another. At their worst, they are terrifying. At their best, they are incomprehensibly devious, immensely frustrating... and terrifying. They are busybodies who can't mind their own business. They love pawns and PCs make wonderful pawns. Voriig Kye is by far my personal favourite. I love to drop him where the PCs are, as a white-haired stranger, and watch my players scramble even though the characters themselves have no idea who he is.
In my opinion, Duranaki are minor players on a grand scale. Their collective influence becomes significant only if the PCs are in or around Tanara.
And Unlife... I usually present a duality about Unlife: the minions who follow because it suits their own twisted desires or urges, and the minions who follow because they have found the true faith in nihilism. The first tend to be very aggressive, mentally deranged (if possibly quite intelligent) in more than one way, and, in short, ruthless bastards. The second tend to be polite, enlightened, ready to discuss theology and the comparative worth of beliefs, and can really turn someone around. The first will torture and slaughter for fun and to inspire terror. The second will have people kill themselves with a smile on their face. I play with this duality - Unlife can be seen as the ruin of the world, but it can also be seen as the peace of nothingness. A seductive Unlife is often more disarming and terrifying than monstrous opponents. I tend to use Unlife behind the scenes - pawns obeying pawns, plots within plots - if only to fend off mind-reading spells which are plentiful in Rolemaster magic (after all, prisoners can't tell what they don't know). Having the PCs defeat troublemakers, only to discover later that they actually removed people who were opposing minions of the Unlife really sticks the knife in.
If you're not afraid of having the PCs travel quite a bit, using the "plot within a plot" can broaden perspective - start small in Jaiman (for instance in Rhakhaan) and resolve the outer plot, and discover that there is an inner plot with an international scope and travel to Sel-Kai to deal with it. You can also use transcontinental factions such as the Jerak Ahrenreth for that purpose - them not being aligned with the factions local to Jaiman make things even more interesting and difficult to untangle.
One very important point in my opinion: the world does not revolve around the PCs. There are other plots and other events ongoing while they follow their own trail, and stumbling upon events that are not correlated with the campaign plot is, I believe, necessary. The war in Urulan, Ulor stirring in the west and Sulthon Ni'Shaang in the north, trade wars between Sel-Kai merchant princes, the Alliance sending emissaries here and there, and more... even if it has nothing to do with the campaign plot, they set the stage and they tell something about the world.