However political Watergate was, Nixon was still under investigation. Terri isn't. Using a political scandal as precedent for a largely unrelated use of the presidential pardon doesn't strike me as something we should get into the habit of using.
There will be a liberal Democrat in the White House again, after all. It might not be in 2008 or even 2012, but it will happen.
We have already seen how an evil democrat would abuse pardon power.