Hello K5MAP,
This is a great question and I know other folks on the forum have some advice on the the HD option. I do not have the HD option on my LR4, but I did switch out the donut spare with a full-sized spare. As for the locking rear differential, it's probably a good to have, but I know that very, very few people ever use it. I don't think that the HD package would make a difference in towing? I know there is a tow package.
I know several LR4 owners who are pretty ********* off-roaders and none of them have the HD option. They all seem to do really great and have no issues. I do moderate off-roading and have never had a problem - the truck is amazing through all terrain. I would say the locking rear differential is important if you plan to do some extreme off-roading. Is that your plans?
With all that said, if you are going to order your LR4 - go for the HD option since it's not that expensive; however, if you are looking for a left over it may be difficult to find one. I know other forum members have discussed the lack of inventory for 2011/2012.
Regards, David