IMHO it's not really worth it if you don't have the oil to spare. E.g. it makes more sense to invest in Amelia research to get a fifth plane or upgrade the plane for better survivability.
You get just 10% more HP and 11% more DPS for the vehicle, paired with 45 oil increase. I just started the research because it was discounted by 50% a week ago.
Not really worth it right now, but I took advantage of the discount. When the next age comes out, the spawners will be upgraded, presumably, so that will be worth it.