Well, to be honest (not even joking), probably the only thing that would save this arc for me would be if Gray and Mira married and had kids or something along those lines. Even if it is just a chapter where Gray and Mira share a battle together or have a little intimate moment, then I'll pretty much consider that a "save" for this arc.
Apart from what I listed above, there is really nothing else that can save this arc for me. The Spriggans have been one of the most disappointing villains in the entire series due to being falsely and massively overhyped. Even the general plot or storyline has been rather lacking in all aspects.
If you ask me, this arc should be scrapped. Since it's too late for that though, the second best choice would be to say that this was all Lucy's dream or this is Lucy's new hit novel that is gonna be featuring in the most popular theatres in Magnolia.
While most chapters in this arc have pretty much received low ratings in my book, there were a few instances where I actually believed that it was still possible to "save" this arc.
Examples would be like Makarov using Fairy Law & sacrificing himself or August completely stomping all of CS by himself.
August can actually still save the arc if he is the "Mard Geer of Alvarez Arc". So can Acnologia, but if I were Mashima, I'd probably wait until the next arc to give Acnologia the spotlight. Mixing Acnologia in with this whole disaster would negatively affect his character, in my opinion.