Funny, but I've been thinking the opposite. I've been earning enough gems in each event to buy one of the 1500 gem ship offers. I bought one near the beginning of this event for 1500 gems which left me with under 200 but I am now up to 1959. Some of those did come with a $US 9.99 ship purchase, but I think it was only 360.
Yes, I watch ads when 5 gems or more could be doubled, including the achievement rewards. Yes, I join every trophy competition even if I don't plan to make much effort. Usually I get at least 5 gems. Depending on the tasks, I can get 25 even without finishing near the top. I finish all the daily challenges (60 gems/mo or 120 with ads). I work the quests which also give 2 or 5 gems. Plus in this event we had contractors awarding quite a lot of doubloons, which exchange for gems.
And that hasn't even touched on the Global challenges we get in a lot of events.
One note, I pretty much never use gems for anything other than buying or (rarely) leveling up a ship.