I am seriously considering upgrading my DGX-500 to a DGX-635 but I don't know if it would be worth the expense! I would like to have the graded weighted keys and wonder if it's even worth the change. I am an older player and I do not play well...taught myself to play a few years ago but...I do love to relax and play what I can. Does anyone out there know if these keyboards are near identical or have they improved this model some? Yes, my speakers vibrate too at high volume but it's usually not a problem so that apparently isn't any better. Any suggestions would be appreciated. Thank you.