Hey, it's your money. If you've got an extra $120k to spare and want the image of the latest LX, go for it. I'd pay down my mortgage, or invest it, or put it down on a lake house before I'd do that upgrade.
Definitely not worth the significant price upgrade. I think the LX600 is a nice bit of evolutionary progress in the Lx model, but not worth spending a ton of money to upgrade to.
If you have access to an LX600 for anywhere close to MSRP, I'd jump.
I have an LX600 base model and am more than happy with it. Check out my impressions (and lots of discussion) Here.