If your 1999 RR was in stock form, I think you have nothing to worry about with the LR3/4. Ground clearance can be a bit deceiving with these amazing suspensions that just keep dropping when necessary. In off-road height, the LR4 can tackle pretty much any terrain other Land Rover vehicles (again, in stock form - wouldn't be fair to compare the LR4 to lifted rigs) can. It will negotiate the trails you mentioned above without breaking a sweat and without requiring any lift, with just some careful wheel placement.
For the type of unforgiving, sharp rocks you will hit in DV you definitely need some decent all-terrain tires though, because the stock ones may be OK on other terrains but will get murdered in Death Valley, the sidewalls are like butter and there just isn't enough of it to begin with. That can be an issue with the LR4 since no factory wheel smaller than 19" will fit over those large front brakes, and finding 19 or 20" A/T tires with a decently sized and tough sidewall, and that will fit the wheel wells of our cars, is not easy. You will find many suggestions on the forum.
Personally, I decided to purchase a set of aftermarket 18" wheels that fit our brakes, since there is a much better selection of beefy 18" tires to choose from. I live in SoCal and go to Death Valley as much as I can myself, I love it there! I am also getting underbody protection - rock sliders and skid plates - so I can tackle the more challenging stuff, but you can negotiate 90% of the trails in that area in stock form, with just better tires than what Land Rover supplies. Beefier tires will also increase your ground clearance a bit, of course.
Finally, you can gain a couple of extra inches of clearance for more demanding rock crawling with either mechanical modification (such as shortened suspensions rods, search for "Johnson Rods" on the forum to get an idea) or electronic ones, such as EAS Control and IIDTool - not quite available commercially for the LR4 but it should be a matter of days now - or my Llams module from Australia.
Are you a member of SCLR by any chance? They are going to Death Valley this weekend with a Dept. of Interior Geologist leading the way... I was going to go - would have been my fifth outing there - but had to cancel due to family schedule conflicts, which really ****** me off... I like to avoid the summer months there if I can, for obvious reasons. SCLR normally has another DV Geology Tour in the fall, I won't miss that one for sure, and you should join us too. It's a great trip and Death Valley is always spectacular to begin with.
