From my "non scientific" watching of MH's for sale on eBay, Pinside, Craigslist & at shows over the last year, I'd say I'm with the 50/50 crowd.
I fully believe probably all EM's due to early production had the inscription, & somewhere along line in SS production it was phased out, my guess would be about 1/2 way through...
My SS which I don't have serial # for here at work, did not have the inscription originally. I installed a mint NOS glass with the inscription. & Then I found another decent glass with inscription at an auction & bought it as a wall hanger in my pinball room.
But of all the machines & glasses I have looked at, I'd say it is around 50/50.
I also agree that a machine with the inscription probably would be worth IMO $100 more than a non inscribed machine.... just for the pure value of another Dave Christensen Easter Egg etc. I always show people the difference in the 2 glasses when they first see my machine (most people who check out my collection are just friends who are not pinheads) & it's just an interesting conversation starter. I show them the dude banging the chick in the tower in Nitro Ground shaker, the Artists face & Jeep on my Silverball Mania etc. To me those are just interesting details that make pinball art from that time period more interesting. Faris put "Farisbuilt" instead of Peterbuilt on the grille emblem on the tractor trailer on Night Rider etc.