Spaying is definitely more common in the US/Canada than it is in the UK. I know that I wouldn't routine spay them though, for a few reasons. It is a big operation, very intrusive, and it's usually very painful for them after the operation. They'll need strong pain relief and not all vets seem to give the right medicines. Speaking of vets, you need a really experienced vet who is going to do the operation properly. With neutering boys it is just a 10 minute operation - spaying is opening them up and a lot more tricky than that.
There is no proof that spaying completely stops tumours.
There are people who have had their girls spayed and still ended up with them getting tumours.
It doesn't stop all types of tumours, only hormone related, obviously stops pyometra as well.
My vet wouldn't spay rats routinely and I really value her opinion.