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.
