I assume G0-T0 can adapt... but only to things he knows. He has of course a huge data base and can hack into other data bases. He developed all these ideas to deal with the situation he was programmed for. We don't see G0-T0 dealing with a situation which is completely new to his programming. Maybe on Malachor, but he isn't doing much there.
Plagueis would have to figure out which situations G0-T0 can adapt to and which he can't.
Your argument might make sense if
a.) GO-TO's programming wasn't broken
b.) GO-TO didn't have a personality
You say GO-TO has never adapted to something outside his programming. So what is his programming? To monitor and advance the Republic's interests by aiding Telos IV.
Nowhere in his original programming did it tell him to leave Telos, create a smuggling ring, get a deadly and cloaked body, set a bounty on Jedi/Sith, join the Exile, go against his allies on Malachor, or make any number of choices. He was not programmed to run a criminal organization.... so how are these feats "ideas to deal with a situation he was programmed for"? Going from an droid overseeing a planet to a criminal overlord seems like a completely new situation to me....
Basically, GO-TO is alive. Droids that gain personalities due to lack of memory wipes are, at least in the mental sense, living. He makes choices on his own accord. His code is broken and he has a personality, along with extensive knowledge. He would be just as good at countering Plaguies's tactics as any other schemeing criminal, if not better.