It is a shame that after all the trouble nursing your last set of batteries along, you are still not out of the woods, and you should be for the money spent.
Nobody else knows what is worth it for you, but I know I am so happy I ditched those 27DCs that I was spending too much time and effort keeping going, even though they were still "going."
If the money is there, IMO don't be stubborn, and take the "easier life" route. Perhaps a second one of those AGMs would suit, since you like that one. Anyway, unless you are strapped, remember you were not put on this Earth to nurse a 31 battery! :(