I have number of EHM (then Archival Matte) pieces from 2005 framed with the print in contact with the glass, and backed by foamcore. If there have been any qualitative changes, they have not been to the worse. No sticking to the glass, and when removed the prints are flat as a board. I haven't done any measurements, to my eye the unprinted areas still look satisfyingly white. But this is in a very dry climate, albeit with relatively cool, high humidity interiors when the evaporative cooler is running during the summer. I wonder if the direct glass contact somehow mitigates chemical degradation of the surface. But don't try that with glossy prints, this I know.
With optimal post processing you get a very handsome looking image on the better matte papers, which in some ways make their glossy brothers look rather crass. If you really wanna see some nice lookin' matte prints, try Epson Cold/Hot Press, BC Elegance Velvet, and a few others.
BTW, for those of us pondering the glass/no-glass question, Elegance Velvet takes Glamour II very nicely, but the Epson papers don't, and sadly that includes EHM and all the other micro-porous papers. I just wish Elegance came on a substrate with 1/2 the thickness and 1/4 the curl. You'd think inkjet paper designers never had to deal with those stupid, high-GSM, hi-curl rolls from the user's perspective. Kudos to Canson for 210 GSM Rag Photo rolls, but it doesn't take coating, sigh. Am I Off Topic yet?