Hi Tony,
Guess I will be the first to reply to your request for ways to improve your playing skills. I speak as a novice keyboardist and can say that only through hard work am I able to gradually improve my skills.
I have found that playing scales is the only way to acquire agility, independence, strength, and evenness in the fingers. There is no way I could hope to play improvisations without those fingering qualities. I play scales every day for about 20 minutes before beginning my normal practice. I am using the "Hanon Virtuoso Pianist" book of exercises, but any book recommended by your dealer will be fine. In my view there is no substitute or shortcut way to acquire playing technique. Playing scales is essential.
Sightreading is a skill that takes quite some time to acquire. There are sightreading books available if you want to purchase them. But if you have "easy" level books of music, they will do just as well. I pick up an "easy" book and just play page after page, almost non-stop, mistakes and all, and I find my sightreading ability is gradually improving.
Remembering tunes is something I found difficult at first. My approach has been to play my repertoire of songs every day and in that way I refresh my memory constantly. I haven't committed many songs to memory yet. I've concentrated on just learning to play. David Ash, who writes for Keyboard Player magazine, wrote two books in the mid-80's. One was titled "How to Play Keyboards by Ear" and the other "How to Remember Music". I don't know if they are still in print. Your local bookstore could check for you. The ISBN number for the first book (playing by ear) is 0-9509477-3-3 and the ISBN number for the latter book(remembering music) is 0-9509477-1-7. If I were you I would send David an e-mail and ask him if he still has copies available if your bookstore cannot obtain them. They are excellent, easy to understand books.
Finally, I tried learning to play on my own and was not very successful. Just before Christmas last year I engaged a music teacher. My playing skills are improving significantly because I am receiving proper instruction and the pressure of having to have a lesson ready forces me to practice hard. I find I am enjoying my music so much more because I can play pieces I couldn't have attempted a year ago. I have a KN6000/EW65 with all the footswitches, the expression pedal and the Technote Organ Workstation. My teacher knows Technics keyboards and how to use all the accessories and he is teaching me to use the organ pedals as well, so I am also playing organ music. Its great fun. I strongly recommend formal instruction from a competent music teacher rather than trying to learn on your own. You will progress much faster and enjoy your music more. Also, you will not pick up bad habits that are hard to break or which restrict your playing ability as you inevitably will if you try to learn on your own.
Hope this helps, Tony. Take care.
Chuck