welcome to the family, wannabe!

no, i do not think memorization has anything to do with musicianship, but it is an indication of experience (or lack of). This just takes time and lots of patience, which you claim not to have.
I can still play some pieces well (OK, somewhat reasonably well), just not memorized. This is my greatest weakness in playing, i.e. among other weaknesses. The problem is that because I'm not trained in doing this (although I have done it for piano juries), it takes me too long, and hence by the time I'm partway through a piece, I have lost interest in it, because I'm not very patient.
It took me years of daily practice to develop memorization skills. if it (and sigtreading) were so easy, more people would be musicians.
Bennom's first post is a bit insensitive, claiming your question was stupid, but he makes a good point about musicianship not depending on memorization.
it's really not that hard, but it is made easier if you know your chords and fingering. it also depends on the composer (Mozart and Chopin are very difficult to memorize, in my opinion, while Rachmaninoff and Liszt are easier)
For those who play for their own enjoyment - when do you move on to something else? For me, the music has to inspire me throughout the period I play it, or I can't continue with it. Some pieces have more lasting effect than others. What are your experiences?
Well, think about concert pianists. Van Cliburn, for example, has played that Tchaikovsky Piano Concerto for over 30 years! I wonder myself how one can stop from getting so sick of playing the same piece over and over..
then it hit me- they dont practice it all the time! Like myself, I have been working on Hungarian Rhapsody No. 2 for over a year now. A month ago, I played it for my teacher (because I have to play it in competition in May.) He told me that it felt like I subconsciously tried to add little annoying mannerisms to the performance to make it more interesting for myself. He told me that the piece was going stale from overpracticing and lack of interest on my part. He recommended that I walk away from it for a while (like a week maybe) and come back to it. Of course, I would have to come back and maybe relearn a few of the notes I had forgotten from lack of practice, but musically, everything comes to me fresh and it feels like a new piece!
and since I had learned it once before, it didn't take long to get it back to it's technical state again (a piece I havent touched for 4 months takes me maybe 4 hours to get back). I think this is how pianists keep a piece for a lifetime without getting tired of it.
Learn new pieces if you feel you want to. and then, after having the satisfaction of learning something new, go back to what you left behind. You will find it very easy to get up to par again, I promise! also, you will have new ideas, as you have forgotten the ones you got tired of before.
Now, the fact that you struggle with memorization might make this a little difficult at first, but really, time and practice is the only way to improve. Not to mention that adults don't learn new skills as easily as they could when they were young (Josef Hoffmann makes a depressing little chart in his book "Piano Playing"). But it's still possible, and always well worth the effort, so keep at it!
donjuan