Anyone think these are worth keeping?
This may be a dumb question, but here goes. Did you ask the seller what was the origin of the speakers were? Did he have them built, or buy them like that? Were they "custom made" for him, or made for sale? If he bought them new, and they were made for him, he should know what he paid money for. Just a thought.
Now that you know how to get inside, why not see how the speaker is mounted to the baffle, and remove it. Get a look and post pic's of the front of it. Also, if you have a multi-meter, you can check the ohms of it. I'm guessing it's 4ohms, like a car speaker.
Worst case, if it's a car speaker, you can replace it with a better 2 or 3 way (speaker), and you might enjoy them the way they are. If not, the people here might be able to suggest real hi-fi drivers that would work in that size cabinet. The only "downside" will be getting those grills off intact, 'cause you'll have to cut new holes for the drivers.
And if you go that way, I DAMN SURE wouldn't want to you getting those grills off. LOL
Good luck.