He's obviously not worth the money, he's a great player. Probably top 5 in the world, but one has to understand the potential. They are suspecting that he's the next Ronaldo and the money they put on him will add to his fame, which in term will add to the interest to see him play. Which will capture mad fans and viewers all over the world, which leads to a lot more TV-revenue and merchandising. It's a common practice for Florentino Perez who erased Madrids debt back in the days through buying very expensive players.
Not everyone can move like this though, Madrid and Barcelona are essentially the only teams that can take these type of favorable loans.
So in the end, Bale for 130 is probably cheaper than buying someone like Higuain for 55m.
players clearly better than Bale at football:
Messi
Ronaldo
Neymar
Hazard
Suarez
Neymar is the only one who is arguable, but he's not been proven in the majors yet except for with the national team.
Recall Robinho? He was just as hot as Neymar, came to Europe and apparently he wasn't the next Pele as Pele had put it.
lets extrapolate this.
Gareth Bale had a hot 2013, 4 months and is 24.
He flipped that 4 months of play into a $132 million transfer.
John Wall had a hot 4 months in 2013 as well and is 22. He would cost $200 million.
He was voted player league player of the year for his 2010/2011 season
.