I don't want to make comparisons, as I feel that both Mette-Marit and Charlene are individuals who come from different lifestyles and countries, I felt the need to correct some of your facts.
Mette-Marit did graduate from the Norwegian equivalent of high school. True - she spent a semester of high school as an exchange student in Australia, but she went back to high school afterwards and completed it. Among her uncompleted education is an college-level construction engineering degree. She also has followed classes at the University in Oslo, as well as studied at the School of Oriental and African Studies when Haakon and Mette-Marit lived in London.
And it seems strange when honest jobs, even strawberry picking and waitressing on the side of pursuing an education, are put down as being bad for your future reputation. But yes, she did have a child out of wedlock - as have certain royalty had. The bottom line is that Mette-Marit is doing an okay job now- and I agree with your point that Charlene also might do so. Being molded into the royal fold takes time. Charlene might have an easier time than Mette-Marit in the beginning (not factoring in Mette-Marit's broken leg, pneumonia and really bad sun-burn) in that she's attending events now as Albert's companion, while Mette-Marit didn't attend much of anything official with Haakon until they were engaged.
As for Charlene - I think it is wonderful that she had the guts to go for her swimming career. It might have been something that could have been combined with finishing high school - but as it stands now, it wasn't, and that is in the past. I'm sorry if people think she's a golddigger simply for going after Albert - it should be pointed out that looks aren't everything when it comes to falling in love. I don't think Albert is bad looking, though. He seems to be an interesting man - having competed at the Olympics, and such.