FYI - The Item upgrade weekend closes today. And the Breach event ends this Friday. I probably should have pointed these out earlier, but I'm not sure if more than two people are reading. I guess I'll try to do these in advance, regardless.
First week of April is First Contact day, which for some reason runs for 5 days. No announcement on goodies that I've seen yet, but looks like some cool stuff has been given out in past years.
There's a shuttle PVE weekend after that. I don't think I knew there were shuttle-only missions, but those have extra awards.
And then starting on 4/20, there is an Elachi Alert weekend. 50% more marks for those missions, so if you need rep that's a good time to grind.
That's it for April, as of today.