I would have to say as a kid, I never paid attention to back variations. The series were so short-lived in the stores that I never got different backs in the few series that had them. I wasn't aware until years later when I saw it in a non-sports guide. As I said before, the only back variation I've seen that adds to the sticker itself is the coupon but only when it's a coupon for the sticker on the front. I rarely even looked at the other coupons. I think the puzzle is outdated too unless it's on the checklist, but even that seems redundant.
I'm not really sure why I got hooked on wackys. I don't think it was their being "racy" that did it. I certainly didn't think any differently about alcohol-based wackys or even cigarette-based wackys because it was only a few years after tobacco advertising was banned on television, so I remembered the commercials. It's our politically-correct culture now that says these things are taboo, so I'm not sure what would make them more appealing to today's kids. I have handed them to various kids, and they were only really interested in the products they could identify, so maybe that's an answer.
I would venture a guess that those of us adults who are still hooked have some sort of "wacky bone" in us that makes us like that kind of parody. If that's the case, then it would limit the kids who get hooked today. Either way, I'd love to see them in stores again because I agree that opening packs is the best way to collect. I also like to keep some product "unopened" to preserve for posterity.