I tried planting the seeds a couple of years ago, and what I got was smaller and the skin was thick and tough, and as far as taste, you could tell it was some kind of squash, but didn't resemble the parent.
If the squash was an "heirloom" type to start with (the variety breeds "true" every year), and planted far enough away from any other squashes to prevent cross-pollination, the seeds can be planted the next spring. Just choose seeds from the best (biggest, sweetest, etc) squash(es) you get. (make sure the seeds haven't been cooked, first, as in softening the squash for easier cutting,,,)
As for roasting and eating the seeds -- Yes! They're just like any squash, and that includes pumpkins: The seeds are very edible after roasting. Add a little salt, and...yummy! :-D