A good indicator if you're ready?
Prove you can play at least a couple other Beethoven sonatas (not Op. 49, either) well. I mean like the Op. 31 sonatas. One of the late ones (Op. 109, 110, 111, for instance). And not only Beethoven. To give you an idea of the scope of these pieces, try the Chopin sonatas/ballades, the Liszt Hungarian Rhapsodies and Paganini Etudes, the Bach Partitas.
If you can conquer these, than you are ready for the Appassionata.
Baah, I work with the Appassionata without having done all that. Ok, I have left mv 1 on the to-do-list, and it will probably remain there for a long time, but the other two movements are not that hard. Well, not that they are easy, no way, but I feel I can get a grip of them with just "some more work" ... and things is, that I love to work with them so it is not work at all to me, it is just sheer pleasure and that is also why I do it: for pleasure.
Not for presenting this brilliant pearl for an audience later on. That will probably never happen. There are millions and millions other pianists out there who do it sooo much better than me. But to me, the Appassionata is the best piano work ever written. It is like tapping Beethoven's soul, his innermost feelings. That is what he is exposing in this music, IMO. When I listen to it, I can feel the joy, passion, sorrow and rage in such an extent that it often bring up tears in my eyes. He is telling a story in this sonata - not a story with a plot, but a story about emotions.
There is not other composer who has managed to expose his/her emotions in that way, who has the ability to express a thought and an emotion in practically every note and harmony. It does not matter how often I play or listen at Beethoven; I always seem to discover something more in the music, yet another layer. That is truly fantastic and that is why I adore Beethoven so much.
Yes, there are so many terrific composers that I also love, but there is something between me and Beethoven

I would probably have disliked the man if I'd met him in person, but this is not about a person, at least not a physical and mortal one. Maybe it is about a soul. I find it most interesting and thoughtful that this dark and repellant individual - as he seemed to be - could reveal such a beautiful and glorious spirit in his music. Like the ugly duckling, you know.
So I keep on playing these magical chords and leaps in the Appassionata and if you believe I'm "wrecking" it then go ahead - I am just ENJOYING myself.
Oh, and by the way: HAPPY BIRTHDAY, Ludwig!