I'm with the 'let it be' group. If you add appliqué or machine quilted designs, you are making it your quilt and not your mother's. The design is beautiful, just the way it is and it is clearly from her heart.
If you ask her if you can add some appliqué, of course she'll say yes, but I suspect she'll be sad that you don't like what she made for her great-grandson and think it unworthy. It's just not worth the risk.
She asked for help with the binding, so do that and if it really needs to be made more secure for washing and use, make some very unobtrusive cross-stitches in the open spaces...not knotted floss ties with tufted ends.
Just my 2¢