How much value does double vanity add to SFH

[Brian Cheng]

I just toured a place today that i really liked, the only thing about the place is it's got a single vanity sink for the masterbath( the bath itself is quite small and doesn't have space for me to change it to a double). Everything else looks quite good, the house's built in the 70s so it looks dated and needs cosmetic TLC.  How much value/how important is the double vanity adding to the house?