If it's 3-4 times bigger than the Uranium, and Uranium will last us 10 more years - Thorium would last us 30-40 years. What to do after that?
If there ever appears a new intelligent civilization millions of years after humanity, they'll be very disappointed to be on an Earth without any Uranium or Thorium!
Uranium will simply not run out. The "10 years" figure stems entirely from misunderstanding what the word "reserve" means in mining.
Also, there is 3-4 times more natural thorium than natural uranium. Of natural uranium only 0.7% is U-235, which is useful in a traditional reactor. Breeders can use all of it. Thorium reactors are all breeders. Assuming only resources extractable at current market prices, using uranium breeders the reserves would last ~1400 years and the thorium reserves would last ~5k years.
