A rather interesting and untestable generalization. I would say that Spivak's book certainly does not fall under this category, since several generations of future mathematicians have been taught from it already.
I too know of no solution manual for it. I would say though that, unless you are Ramanujan, it is rather difficult to learn this level of mathematics on your own. The ideal situation is to take a course in it. Nothing beats having an actual instructor to discuss these things with and have different perspectives of it shown to you. If that's not possible, then the next best situation is to form a study group. This is a very challenging book for many people and it really helps to learn it with other people.