Your L38 Machamp are already at a good level, so that's not imperative, but also not too costly. You might want to just knock those out. SC/SB Gengar and Blissey too. You've already gone that far; just finish them out.
Of the remaining, I wouldn't spend dust on anything except Gyarados (good to have one even if you have a powered Kyogre).
The ones I would NOT feed are Beldum, Slaking, and Donphan. None have any real use at the moment.
The rest are situational and up to your discretion and game play.