To be honest a denim being selvedge doesnt guarentee its absolute quality, however the denim made on older vintage looms at least gives you some confidence the quality is more likely and the look of the produced denim is more unique and uneven. It has imperfections which denim freaks love. Having worded selvedge doesnt make the denim any better but its a more complicated manufacturing process so it gives a little more Kudos to the brand plus you know the denim was bespoke made for them and not just a generic made selvedge.
As for RMC, there are only a few with worded selvedge, The Heineken Red Star RMC's, the Tropsicle RMC's, the recent Mad patch all have it, there a few more but off the top of my head I cant think of them, but certainly its not common, but I like it, I think it adds a nice touch to the product.