The LXD is deffinitely worth the extra. I had an LMD70 for a few weeks and swapped it for an LXD70, it really is a massive difference. The 100Hz seems to work well with the content I have thrown at it, there is less motion blur on the LXD70. Gaming works well on it.
The thing that made me swap from LMD to LXD though wasn't the 100Hz, but that the LMD viewing angles are not great in the vertical plane, so if you walk past the TV fairly close (like if it is in a bedroom), the picture fades. This does not happen on the LXD, at least I can't notice any fade, even at fairly extreme angles.
The other big difference I noticed is that the LXD70 has noticeably darker blacks (having compared both sets in my home with loads of different content) and slightly more vibrant colours.
The LMD was a very nice TV, but for me, the LXD is in a league of its own at the 32 and 26 inch size, and was worth every extra penny given that I plan to keep the TV for a number of years.
Worth noting as well that in most shops it was quite hard to see the viewing angle differences due to the bright shop lighting, and bright content being shown. On darker stuff in a home environment, the difference is significant.