I didn't think that the fizzy lifting drinks subplot was necessary in the original (Wonka could have just sent them away at the end, saying that seeing his office was the prize, or some other trinket), although IIRC, it was the grandfather who suggested trying them, so Charlie was still beyond reproach. I think Dahl might have been pissed that the movie did a better job telling the story than he did.
While we're on the Dahl topic and as an aside, my wife and I went to look at a house in one of the nicer areas of our town. I noticed a lot of Roald Dahl books everywhere and thought they were big fans. Later-on I learned they had the same last name and were related. No big deal, just kind of semi-interesting. Unfortunately we didn't like the house, because I would have demanded a signed copy of one of his books as part of the deal!