To be honest, most of my experience with the old RoR was slotta-age. When I first got into Warhammer the only Citadel minis I could find were boxed sets. (I'm in the US, so I started off with Ral Partha & Grenadier.) So in terms of Citadel, I started by collecting most of the slotta RoR and Machineries of Destructioni. These hobgoblins, Knights of the Cleansing Flame, and Grom's (and I'm going to disagree with you here - I really like the slotta Grom unit, especially the musician

) were the only ones I didn't have back in the day.
Sadly, most of those old units are gone now.
I'm developing a renewed interest in the RoR. Obviously. I see Notlob's Artillery pop up every so often, and at some point the price will be right for me to grab a set. The half-orcs seem a bit (er, a lot) more elusive. Honestly, so do all of the Citadel half-orcs, unfortunately for me. But I've been pretty happy with the alternatives I've been rooting out.
I'm still enamored with the idea of creating my own Regiment(s) of Renown at some point, too.