National stadiums are largely a useless idea, and a waste of money.
Scotland, with a population a little over 5 million, spent a fortune on Hampden when Glasgow already had Ibrox and Celtic Park. One already had the highest UEFA rating at the time and the other much larger. Edinburgh already had Murrayfield and smaller stadiums (Tynecastle & Easter Road).
The only time that having a national stadium is actually enjoyable is when it is being used for big domestic games, so Cup Finals. There is no difference to watching England play at Old Trafford or the Emirates Stadium than at Wembley. There is a big difference in going to watch your team play a Cup Final at Wembley than at some random neutral stadium.