If you plan on keeping the vehicle past 50k, an extended warranty would be a good idea. Mainly because the cost to repair anything which may go wrong, can get costly. My dealer generally charges around $100 for oil changes if you didn't purchase the vehicle from them. I would assume, that's pretty competitive with other dealers?
Wow, you've been robbed. You should complain to LRNA and get your Benjamin's back! The service visits are free up to 50,000 (actually, it's every 7,500 miles, so it's really only up to 45,000 miles that service is provided). Doesn't matter where you bought it, as long as it's a LR dealer that is doing the service. They bill LRNA and get reimbursed for your service costs. They are getting paid twice in your case. You've got a legit complaint.
As for warrenty, I would reccommend them normally, and certainly with a Land Rover, but the warrenty company under contract to LR has recently quintupled their rates to ridiculous costs. I am not sure it's a fair trade off anymore. You are talking in the range of $4,000 or more these days.