I never read the book series but I really enjoyed the movie. Maybe isn't the best that disney have made but isn't defenitily the worst, so I do agree that deserve more credit to it.Â
Making Eilonwy a disney princess could help the movie getting more atention, but I'm afraid that would wash out the movie itself by giving atention only to her, which is not necesseraly a bad thing but I would prefer the entire movie being apprecieated than only one character.
I think if they make a live-action remake more like the book series it would help the original movie getting more atention, because, at least where I live, when they are close to realease a remake they do and sell a lot of merchandising of the original animated movie and that would give the chance to new audience know about it.
This is just my opinion, I'm new at this and since I really liked this movie I just want to share it :)
P.S.: I'm not an english speaker, so sorry for any linguage mistakes i've made :P