I was speaking of certainly valid yet illicit rites that existed prior to Vatican II. Does that help?
In understanding that we should be concerned about both validity and licitness, yes.
But, how does that apply to NO Eucharistic Adoration? I've not heard anyone argue that it's illicit before, so would that not just leave validity as the only concern in deciding whether or not to attend?
Go back to Archbishop Lefebvre's statements on the new mass and sacraments. Those are closer to being a statement of the basis for the traditionalist resistance than anything you or I might say in 2010.
I'd say yes and no, but going with "yes" for the moment, do you know off hand precisely why he thought the NO to be doubtful? I don't, but just bought some big books on him and might just go look it up if you don't have a handy answer for me. : )