I've never heard of the book and I loved the movie.
There was an article a few days ago where Lucas invite Hammill and Fisher to lunch something like 6 months ago and told them he had decided there would be a 7-9... you have to wonder if that foreshadows their involvement? The movie is actually in the exceedingly rare position that unlike other movies, they actually CAN do a story 30-40 years in the future while keeping the same cast. In my opinion, that would redeem the Star Wars franchise for the prequels.
Yep. Bring them back as the "elders" in the series, possibly include a few young punks to carry the torch. It wouldn't be a Star Wars without the generation gap though, of fathers/parents and the children.
As long as it's not directed and solely written by Lucas, there is a strong chance of something good coming out of all this. A New Hope actually wasn't too bad, given it was Lucas at the helm, but Empire Strikes Back and Return of the Jedi were superior and the best of the franchise, and it can't be a coincidence that they were the only two to not be directed by Lucas, nor did he receive top writing credits.
Lucas can be given stars, but can still find a way to let them act like high school drama students destined for the B-movie world. A New Hope had some hints of that but not nearly to the extent that the prequel trilogy showcased.
If someone else had written and directed the prequels, the same cast could have cranked out much better performances. They have shined in other films, so they can actually act. The dialogue was just terrible though, and hardly any A-list actor can perform award-winning work with sloppy dialogue in the script.
I'm not Star Wars rabid fan, but I enjoy good movies - and the franchise has plenty of opportunity to immerse you in a far-away world.
Oh, and it sounds like original concepts for the sequel trilogy followed a 30 or 40 year old Luke. I'm not so sure Mark Hamill could really pull that off now. But I think that was from the original stories back when IV, V, and VI were still fresh. Lucas may have altered those plans in the treatments he provided to Disney.
edit:
This got me thinking: who would we prefer to have the director's chair in the new series? With his - imho - successful production of Star Trek, among other things, I think J.J. Abrams could be a good fit. He doesn't necessarily need to be involved in the writing process, though he could lend a hand there. I have a feeling this wouldn't be happening though, as Abrams might be fairly tied up with the Star Trek series. It would be interesting for him to have credits as director for both the current/new Star Trek series as well as the new Star Wars movies.