Look at the credit numbers. They're much, much higher than the other objectives of that level. For example, on the very first mission, Jabim Escort, destroying the bridge of the capital ship awards you 2538 credits. It requires either proton torpedoes or some serious skill with missiles. When you get the torpedoes at lvl50, 2.5k credits is not a whole lot of money, but it isn't insignificant (about as much as a loot chest or a single quest). It seems to me that the purpose of the extra objectives is to make the mission worth doing - or at least not a complete waste of time - at max level.

I just did the three highest-level missions and can report the following: Note that all of these were done at lvl50, only once each today. Aeten Defense (higher level version of Skaross Fortification) Main: destroy bombers Bonus 1: destroy fighters (30) - 2411 credits Bonus 2: destroy frigate shield generators (4) - 2511 credits A proton torpedo hit to the capital ship's bridge did nothing. Clouds of Vondoru (same as Serapin Assault) Main: destroy capital ship shields Bonus 1: destroy fighters and turrets (75) - 1526 credits Bonus 2: destroy the capital ship's bridge - ? credits Destroying the frigates' shields did nothing. Ascendancy Barrier (same as Polith Minefield) Main: destroy mines, destroy mine layer Bonus 1: destroy heavy fighters (4) - 2943 credits Bonus 2: destroy fighter tender engines (4) - 2943 credits There were no possible targets for proton torpedoes. We've seen extra bonus missions open up later, past the intended levels of the space missions. I did not find a third bonus in any of the three intended to be done at lvl50. I think it's plausible that BW will add a third to each of these at some later date, perhaps in an expansion when the level cap is increased (and these missions grey out). Also, destroying the capital ship's bridge on Jabim Escort yielded 2538 credits, as did dong so on on Sullust Interception. Destroying the capital ship's shield generators did nothing. Is there anything else you'd like tested?