Cleaning would certainly improve them. Olive oil has the benefit of altering the patina by darkening it, which I think would help these.
First things first, they need proper treatment if they have had BD (though I think this might be a different issue, just an inherently weak patina). I would usually advocate using distilled water for the treatment, but this is slow and if they are this badly afflicted, then it is too late for the soft option. You can buy chemicals to treat with, or you can try using sodium bicarbonate (bicarb of soda). Get some water (doesn't really need to be distilled in this case, but I would use distilled anyway) and dissolve a bunch of bicarb in it, put the coin in it and heat it. Turn off the heat when it nears boiling and allow to cool, then give it a brush with an old toothbrush. For this case...repeat that a few times and leave in the mix for as long as you can. It might come out with a patchy looking patina and a cratered surface, but there isn't much to be done about that - the damage is already done. A year or so in olive oil should even it out to a uniform black colour.
In terms of value, that bottom one looks like quite good work. It might come out well - not a high value coin, but not a junker either.