Also, I should add that I don’t allow non-career specs, so my players have to get creative at using the specs in their careers, rather than cherry-picking the best ones.
Eugh, but then your Commander Tactician will never get access to Suppressing Fire or Prime Positions, which I could gripe about for hours . That said - and going by the rule that all XP expenditure should make sense and contribute to RP - cross-career characters are my favorite and become generally very interesting when justified well. My Commander Tactician might finally accept that open invitation to be part of the Urban Guerrilla's SpecForce group (which he'd been ignoring because "his squad needed him") and pick up the Soldier Commando spec. The Force sensitive who crash lands on a desert planet and discovers he's a Seeker Pathfinder before the game starts might have spent most of his life as Smuggler Pilot before being betrayed by a contact and shot down, so he'd spend his XP on both specs. My Warden might decide punching things too much will lead to the Dark Side and start to dedicate himself to ending fights in the "peaceful" way of ensuring there isn't one to begin with... because everyone's too scared to try anything. So he may decide to pick up Agitator or even any of the other specs with Fearsome. If you want to play a dedicated martial artist, it helps to have cross-career access.
But, with 20 characters, allowing cross-career specs would probably create a lot of agonizing overlap. So there's that.
Back on topic! What wouldn't I play? Entrepreneur or Gambler. I'll admit, every spec has it's place in someone's game, but I just can't see these being interesting to me at all. I've never been much into the economics of the game, though; it slows down what I and my players generally find interesting... so I'm biased. If I ever get around to starting the idea I had for a numerous-player PC-run colony based on Homesteads and Businesses and space stuff, then maybe those characters could see some use. But it's a game designed specifically so that players can try out specs that never see use in traditional games.