The Spice Girls were the biggest band of the 1990s, and that's not my opinion at all. This is an argument that it isn't even worth having.
They have sold 75 million records, making them the number one girl group of all time. Their live comeback was "better" than the one mounted by Led Zeppelin and The Sex Pistols. They do have some credits to back them up.
I am only marginally interested in the Spice Girls. Never bought the music, never paid attention to what they did, but I will acknowledge them as a cultural movement. They are largely forgotten now in the United States, but, in Britain, these ladies were all the rage on the front pages of the newspapers and in the celebrity gossip machine personified by Rupert Murdoch's papers and all of his competitors. Their lives were pulled apart and examined and it is still, to this day, impossible to understand how Victoria Beckham keeps it all together. What woman on Earth has been hounded more than Beckham? Well, Melanie Brown and Geri Halliwell might want to get in there for a word. Emma Bunton and Melanie Chisholm didn't exactly get a free ride from the press in the native country, either.
In any event, they are playing for the Queen. This means something in Britain. I don't think it will merit more than a yawn in the States. Perhaps there are legions of hardcore Spice Girls fans in the Midwest. Who knows?