DannyUK: I think ALL the keyboards you mentioned (including your X1) are still EXCELLENT keyboards cabable of making PROFESSIONAL sounding music. The NEXT new model keyboard is NOT going to make you automatically better. This is only a marketing ploy used by the manufacters to keep you buying. Time spent practicing, and possbily taking some keyboard lessons are probably a MUCH BETTER investment than thinking the NEXT keyboard will be better. REMEMBER, the musical expression & creativity comes from US, not the keyboard.
That being said, I personally prefer the acoustic piano sounds and ease of use of the Yamaha 9000pro & Technics KN boards over the X1, but these are 'very personal' preferences. The key is to enjoy MAKING MUSIC on whichever keyboard you currently own. Switch ONLY if you no longer enjoy making music on your current board.

- Scott