I was on the Navi from 4/27 - 5/13, and that included all the itineraries. The number of passengers fluctuated from 900 - 3,000. However, the 3,000 cruise was over Mother's Day weekend.
I would NOT recommend a 3-day holiday weekend cruise, and not because of the crowds. The ship is plenty large that you don't feel crushed (except maybe on the pool deck). But, it was party central, for sure. I'm OK with that, but when you have 1-3 Alpha calls (medical emergency) per DAY, with a large portion of the passengers under the age of 40.....well, draw your own conclusions. Also, on debarkation day on 5/9, I was unfortunate enough to witness a young woman being escorted into the elevator lobby in handcuffs. With 6 security and port authority officers.
So, the remainder of my cruises were fabulous. I love the Navi, the food was excellent in the Windjammer, Main Dining Room, and specialty restaurants. Crew is great, too.
Ensenada is meh. Read reviews before you buy shore excursions in Ensenada. Catalina is gorgeous, and I always love Cabo San Lucas.
We were told by the onboard booking staff that they will start more 7 night Mexico cruises next year, too.