Back on topic, for a moment.
To answer the thread's title... No. I don't think any processor can revitalize an AM station. People aren't going away just because of the restricted bandwidth. Creating a "wall of sound" these days is a dated concept that's nearly guaranteed to chase people away. On the other hand, I have no doubt that relevant, creative content that listeners feel they need, can still keep a marginally-processed station humming along... at least in some places.
I do think that "good" processing can help keep a listener around though.
I take care of a bunch of AMs like this. When one of them goes down, it's far more likely I'll get a concerned phone call then a disinterested one. I have very few (only one, actually) owners who might say, "oh... just get here when you can".
Declaring AM dead is premature and... wrong. Get out of the city and head East. There are plenty of small AMs out there that are dominant, local and support full-time staffs. A look at the FCC stats shows that, while the numbers are down, AM totals are still within sight of the number of licenses it had at its peak. It is true, however, that for what you get out of it, AM tends to be more maintenance-intensive than FM, the cost of which keeps it at the top of many managers' "grumble lists".
A lot of AM has moved to niche markets. The owners of those stations would tell you their listeners are far more concerned about hearing programming, provided specifically for them, than whether that content is on AM or FM. I take care of some of those as well and, so long as the bill is paid, their licenses and equipment is/are curiously similar to everyone else's.
Sadly though... KJR, Country KAYO and Colorful KOL are gone.