Rambly, you are preachin' the good word. I love Johto and there are so many things about Gen 2 that are close to my heart. (Obviously that's the case or I wouldn't have purchased the rerelease.) Unfortunately, the postgame content isn't really one of those things?
The concept itself is great and I think, if they ever were to do something like that again, they could do it better now. Perhaps it's that my standards too high nowadays but, as you said, the whole Kanto region seems pretty lifeless. It's fun to explore and see how things have changed over time, but it feels very tacked onto the end.
I would be very interested in seeming them revisit this sort of concept, though. With the next main game title coming to the Switch in a few years, maybe we'll see something a bit more grand that we have on the 3DS.
I read up on how to get Celebi, I bought Silver during the time-window, but they also want you to buy one of the Ultra games too, which I don't plan on getting. What a load of garbage.
I was able to use my Celebi code on Moon version. Have you tried that?