Indeed. When thinking about astromechs, remember the rule should be useable - not necessarily great, but functional - on the X, Y. E and X/70.
To be honest, I'd rather get the rest of the 'named' astromechs as uniques than a zero-cost generic. Rebels are supposed to be (a) a 'rag-tag bunch' and (b) all about the personalities of both the pilots and the droids who fly with them. Nothing stops a unique astromech being cheap - "genius" certainly isn't - but whilst with Imperials I like a squad with multiple identical ships and a single unique 'leader', for rebels even when you have a squad of 3-4 x-wings, it feels right that they have a mix of abilities.
The three most important astromechs to get, to my mind, are R5-G8 ("Gate", Wedge's astromech) and "Whistler" (Corran's astromech) as they're actually regular characters in the legends X-wing series, and R2-KT - as she's one of the few officially named ones we see on screen in multiple films (she's in both the Clone Wars and The Force Awakens, meaning logically she's as experienced an astromech as R2-D2).
I'm not sure what I'd suggest for each.
R5-G8 is the only one I have an idea for. He should, logically, complement Wedge. Wedge's strengths are his hard-to-evade attack and high PS, and weakness is his durability (for his cost, anyway).
Therefore, I'd recommend Gate have an ability along the lines of "After you perform an attack that hits, assign an evade token to this ship."
The latter could be tweaked up or down depending on cost - you could alternatively allow a reroll of one or more defense dice until the end of the turn (which actually would make it extra tempting on an E-wing as they have more green dice), either against all attackers or against the ship you just attacked (the latter could be cheap but would make playing chicken against wedge even more suicidal, as it should be).
R2-KT should, I'd assume, be another 4-point astromech like R2-D2. That implies a **** hefty ability, but I'm not sure what would suit. Whilst R2-D2 lets you recover damage, possibly R2-KT might be about avoiding it in the first place?