Hi,
Here are my thoughts on the two, this is only my perspective.
For me, there used to be a huge difference when you jumped from a LR3 or older Discovery model to teh Range Rover. The RR was really polished inside and out. You could really see the nicer detail in the cabin. Overall, it just seemed like a nicer place to be. I can tell you with the LR4, the gap got narrowed quite a bit. I still think the RR is overall nicer, but I really don't think the LR4 in LUX form gives that much up to the RR. Now that the LR4 has a lot of the design elements on the outside that match the RR, most people can't tell the two apart. Not many people in my arrea have Land Rovers, so they call mine a RR by mistake most of the time.
My personal purchase was kind of multi faceted. I didn't have the money to spend on the RR. In fact, the LR4 was a bit of a stretch for us. I can tell you it was quite a splurge to spend $60k on a vehicle for us. My wife has a Lexus that we purchased new in 2007, and I really thought that would be the most expensive car we ever bought at $42k.
The extra room in the LR4 was the key for me. I have three teenagers, so the extra seating was required. Even though two of them are driving and we don't go that many places as a family, we still take family vacations where we need to have the third row of seats. Just driving to Omaha to catch a flight with the five of us and luggage, it's nice to have the size of the LR4.
I wanted a premium vehicle, and needed the space and offroad ablility of the LR4. I hunt, mountain bike, trail run, adventure race and such. The LR4 was a great match for our family.
Rob