Get intimate with that website link I posted. There are JBL speaker service centers everywhere, and experts on them. You can examine foam yourself, and judge its condition. They are fully serviceable and supported.
I just simply wouldn't advise on whether to incorporate them into your home theater or not. You have to be the judge. They need to be on stands. Get them off the ground. These are directional speakers that won't produce the best imaging when reflecting sound off the floor. Issues like that make integrating them into a home theater possibly more difficult, than sleek satellites on stands that blend into the decor better. And as Darkside pointed out, a set of B&Ws with crossover frequencies matched between sub, mains, center and rear should be ideal for home theater.
In decent condition, you could probably sell them on Ebay for what they sold for new. And they weren't cheap. But JBL doesn't make many like this anymore. They do still make great speakers, especially the JBL Pro division, carbon fiber enclosures etc. But not many in those elegant walnut veneer cabinets. They were costly to make. Personally, I would never sell a vintage JBL, and would be one of the ones to take them to the grave as Chris said.
Tom