Moral of story is that if you are doing TATL or intra-Europe trips in Y while a STE+, fly on AF, KL or AZ. The Mrs. (also a PM) and I were Y pax on AZ, MUC-FCO-CTA and return, and got lounge access in all three airports (CTA has a neat little lounge landside; AZ uses the AF lounge in MUC and has a decent sized lounge in FCO Terminal 1. I've also gotten into the shared lounge that AF and KL use in BUD.
Also, the Air France/KLM Salon in IAD is supposed to reopen this spring, and will supposedly be remodeled and enlarged by more than 50%, as they are opening up the floor beneath the current lounge as additional lounge space. It is a shame that DL does not have a SkyClub in IAD, but I've always enjoyed my lounge time in the AF/KL club. Ditto the VS Clubhouse (great food and drink in there), which is not part of the SkyTeam TATL JV.