I just upgraded to the X35 from a HD350 (same as the HD250 but with a glossy black case). While some of the improvements are down to a new lamp in the X35 compared to a half dimmed lamp in the HD350, there are enough improvements in the picture quality (sharpness/contrast/motion) to make me pleased with my upgrade. I've only bought this for 2D use (no 3D glasses or emitter to save £300 in the UK). It depends on the price difference and your budget of course.
"Don't believe everything you read on the internet". William Shakespeare 1615