My twenty-something son, who is a Messi fan and partial to Barca, thought the museum was great. And I, who think soccer is a beautiful game, thought the museum was great. This was a highlight of our Barcelona visit. The museumwas very well done, with a focus on how the club came into being, great players, and great coaches. The field tour (which included a visit for the press room and visiting team lockers) was also very well done.
I recommend paying the 6 euros extra for the audioguide. It is not necessary for the museum tour -- at least for English speakers, as the placards are equally in Catalan, Spanish, and English. (That said, I enjoyed it for some additional commentary on half of the exhibits.) The audioguide added to the experience for the field tour.
There are outfits that sell personalized tours for a higher price. I don't know how much that could have added to the experience, as long as you get an audioguide. I would save your money and buy tickets directly from the club website.