Isn't real question - "Do you think Derrick Doster can hit better than .370/.475 as the LH part of a platoon?"
My answer is yes, with the usual caveats about small sample sizes (made smaller if you're not an NL team) in any given season. I'd guess Doster is .360/.525, career, in 12-15 seasons.
But with Gardel/Washington ahead of him on the ML years and financial depth charts, I'd be tempted to let them play out their contracts and keep Doster in AAA. I certainly wouldn't pay any of their contracts to open a slot for Doster, but if I could get "value"...