Well, steel is definitely harder, and I guess that if you kept running the same chain, the rings would last longer.My MTB tourer has the same aluminium rings it came with back in '95 and I run 4 chains, rotating every 500 miles, but I haven't done huge milage, maybe 10,000.
Of course, on the long tour you are planning, it wouldn't be practical to do this, so the steel ring idea may have some sense.
I just checked the shimano website. The Deore chainset has all steel rings and that's fairly decent I think.http://www.shimano-europe.com/cycling/catalogue/content_prodx.phtml?pid=11050&psid=25
I hope your EXP is turning out ok and best wishes for your grand tour.