If I hadn't mentioned it earlier... the scope of the game is for players to command single ships with officer cards. The point of it is, with missions out there on planets, you go there with your ship and navigate some skill checks with your chosen officers to see if you pass or succeed at the missions and challenges you're trying to overcome. The ultimate goal is for the Federation to maintain stability in the sector.
The base game goes from 2-4 Federation players playing cooperatively. The Klingon expansion adds one (maybe two?) Klingon players... whose entire job is to mess up Federation operations in this sector. Depending on the Klingon persona (Imperial or Marauder), they do this either by accomplishing missions and assignments of their own in the same sector of space (Imperial) or simply following Fed players around, trying to mess up their assignments or hijack posted Federation missions (Marauder).
Here's an example of the board, the game is a 1 Klingon player vs 3 Federation players:
As you can see the Klingon border is more or less a safe zone for the Klingon player but not much else. L-24s at least can operate under the auspices of Diplomacy missions and "Scientific ventures"- even if it makes the Feds nervous. The orange planets you see here are star systems unaffiliated with the Federation and welcome Klingon diplomats. Until war kicks off the Federation players are forbidden from attacking Imperial Klingon players unless they venture into a Starbase or Core sector without a face-up mission targeting one of those planets.
L-24s as the new hotness can make the claim of being a flag of the empire. L-13s, as the old hotness, can't. Moreover an L-13 player in this setup, guarding the frontier, won't do much other than sit there. The Klingon play-style rewards going forward and being disruptive, not camping the frontier.
All that said, perhaps I will model the L-13 at some point. This game is still very much "under development" and it could be that more old ships can work in this kind of scenario. At the moment however, the fat man is just a bit too far.
No... it's not the Klingons who need help with ship content. As mentioned above for the Klingons I did the K-23, but I also have the D-10 and D-18 as possible additions as well (all more suited for the scope of the game than the L-13...). Really the Romulans are the ones who need more ships to fill out their potential craft, since right now their selections are:
White Wind (FASA, Romulan Box)
Bright One (FASA, Romulan Box)
Senator (Klingon Academy, Romulan Box)
Bird of Prey (TOS, All our Yesterdays box)
Z-1 (FASA, The Final Reflection)
I'm considering the Winged Defender from FASA and the Imperium class from Klingon Academy, but both of them are a little too on the nose in a few respects. Other craft, like the FASA V-6 and nearly all the SFB range, feel more like TOS designs than the 2270s-90s period that I'm targeting.