No, absolutely not! Candidates would actually have to campaign in more than a handful of swing states because every vote would suddenly be important. Even if they didn't have a shot at winning a state, it would be important to keep their opponent's margin down in the state.
Swing states are swing states because they have a greater proportion of swinging voters. Since swinging voters will always determine the outcome, candidates will continue to campaign in swing states. It would lead to very few differences in campaign strategy. The only real difference is that in a close election, recounts become important all over the country, not just in close states - so it would likely lead to more legal challenges and the Supreme Court making more decisions like in 2000.
Not really. A national pool would make recounts far less necessary. Not a single election in the past 100 years would have required one, save,
possibly, Kennedy vs. Nixon. Simple statistics dictate that the margins of error decrease substantially the larger the sample size. Overturning a 500,000+ vote lead, even if that's less than a 1% difference, is extremely unlikely.
And in any event, so long as there are national standards and clear guidelines it shouldn't be a problem in the unlikely event that there is a recount. We could even add a provision that if a president isn't certified by inauguration day, then the incumbent president stays on as acting president until a new president is certified.
