As far as Vulcan emotion goes, Vulcans do allow themselves to feel the more positive aspects of emotion.
How many times have we heard Nimoy's Spock mention that he was "delighted", "pleased", and even grin on occasion (Uhura singing to Spock's Vulcan Lyre playing)? They are still rather restrained in it, but they do allow themselves to feel it. I think it is how they keep themselves in balance.
They repress the negative emotions (the Dark Side if you will). Those usually only come out when absolutely provoked.