Do it!
Whether you are prepared or not, go into it and do it - are you a very young pianist?
Every competition that I ever participated in was a good learning experience, definitely - DEFINITELY!
Try to watch as many competitors as you can AFTER you yourself play - watching them before you play can take you out of your "zone", and can influence your performance in subtle ways, often not good ways...
Talk to everyone you can, make friends and connections...
Unless it is a major financial investment, and it will set you back, then you should go and check it out - there's no shame at all if you don't win or place in your first competition, but you will gain experience that you can't get reading the pianoforum, or taking lessons.
Personally I began by losing tiny local competitions, until slowly, through trial and error, I figured out which repertoire and strategies worked best for me. Finally, years later, I was placing in bigger International Competitions - you see? All those early ones that I sucked in don't matter now, because I can at last say that I am an International Competition winner, which sounds very nice on a resume, and I can only say that because I was willing to lose the early ones, but gain experience from them.
Go for it - good luck - and post your experience later for others to learn from!
