I don't know how the McCann's could have done anything any differently. They were given a lot of money to find Madeleine, people wanted to help, unlike the Ben Needham case Madeleine's case went worldwide with the internet etc. They could hardly have put the money into their own account, and being focused on one child the fund couldn't be a charity for other children. It wasn't just the McCann's who decided on the Madeleine fund they had a lot of help with it.
As for meeting the Pope etc. the Pope was interested in the case, I believe it was Clarence Mitchell who organised the visit to see the Pope, were they supposed to turn it down? They were offered a private jet to get there which made it a lot quicker and less time away from the twins. Everything was organised for them, it wasn't the McCann's who asked for anything. Keeping Madeleine in the news was their goal, which is the goal for all parents of missing children. Ben Needham's Mum said in her book she would have done exactly what the McCann's did, if she had been in the position they were. Sadly for Bens mum, there wasn't the internet when Ben disappeared.
They were warned that it would come a time when it would be all about them and not Madeleine, and sure enough that is what happened, I don't think they would have done anything differently though it kept people aware of Madeleine so that if they went on holiday they could look out for her, or people could be living near to where Madeleine was and report it etc. IMO