three quarters of the country are essentially left out of the campaign. Texas will not swing, New York will not California will not etc etc. So the democrats will try to run up their margins in the bigger cities etc whilst republicans will try to run it up out in the suburbs.

Saying that older people are usually more informed may be true but then having them being the ones that are voting leads to its own problems. They tend to have an outsized influence on policy. Younger people are disenfranchised and generally don't feel part of the political process. Not to mention that just being informed about the issues doesn't really count anyway as the ones that are most informed aren't going to be changing their votes. It's the swing voters that aren't really engaged that end up deciding most elections. Then of course if you do get a whole load of people on one side who are engaged then you get things like the republican house. Oh and suggesting that you would end up with more younger people than older people voting is not consistent with demographic trends.

Btw I am fairly certain that paying people to vote or giving them tax breaks would be illegal.

a simple popular vote would be encouraging candidates and parties to have nationwide organisations. Every vote would matter. Not to mention the fact though that under the current system whoever wins the popular vote wins the presidency unless it is extremely close. In which case you would imagine that the popular vote winner should get the presidency rather than the electoral college winner.

btw you really broadened the argument from a simple electoral college and popular vote measure to one where you were including compulsory voting.