Economically speaking, 1974-1977 under Nixon isn't much different that it was under Ford OTL. '74 is still a Democratic year due to the bad economy but it's not a big democratic sweep without Watergate. Nixon probably passes health care reform sometime after the midterms.
Foreign policy is where the major differences might be. Nixon probably intervenes in Vietnam in 1975 despite congress as this is Nixon we're talking about. Nixon overall probably does a lot more in foreign affairs than Ford did.
As for 1976, I honestly would say that would be a tossup. With the economy being the way it was, the Democrats have their best shot at winning since 1964, even without Watergate. However, assuming Nixon doesn't royally screw up foreign affairs or Nixon's rule bending doesn't catch up with him before election day '76, the GOP as a decent shot at winning it. Ford came very close to beating Carter with all the chips stacked against him, without Watergate, the only thing that can hurt the GOP is the economy, and while that counts it isn't everything. I'd say the GOP nominee is Reagan, especially if Nixon passes health care reform. For the Democrats, one things for sure, it won't be Carter. Maybe Udall, Birch Bayh, Walter Mondale, or even (god forbid) Ted Kennedy. Regardless of who wins, the election will be close.
As for Nixon's standing in history, if the break in or any of the other scandals don't come out in Nixon's post presidency, he'll be seen as average or slightly above average. If it does come out in his post presidency or after his death, he'll be remembered as below average. Either way, without the cover up and resignation, Nixon isn't seen as the top five or ten worst presidents.