I made the change I do not regret it.
The L322 is a complex and expensive beast so be prepared that when it does need fixing, it can be a bit of a hit.
That being said, as the L322 is becoming more of a DIY owners car, the parts suppliers are starting to stock and sell a greater selection of L322 Parts at reasonable prices.
You must have your own diagnostics as this will save you a fortune. Be wary of high milers that have not had the Gearbox oil changed.
The TD6 engine is strong and mostly reliable, turbo hoses do pop off and injector loom issues have been documented....the problem on the TD6 is the Gearbox...it WILL fail, it is just a matter of when.
The V8's are strong, but do suffer from PCV valve failures, VANOS noise and cooling leaks....Radiators are prone to leaks, expansion tanks cracking and hoses splitting...but they are simple fixes....rad is about £160 so not to bad!
The V8 M62TU engine is a long standing BMW design so there is butt loads of information about them on BMW forums as well as LR forums that will cover most issues.
The ZF box on the early V8's has niggles but proper maintenance will help keep it running, but like anything mechanical they will eventually get tired.
I have had my L322 for over 18 months now and I have never regretted changing from the P38 - even when I had a string of failures in a row....Fuel Pump, Rad, Water Pump, ABS Module etc.....(all documented on here).
If you can justify the change, I'd say go for it....
there are loads around so choose wisely and check EVERYTHING, and remember the golden rule - Never, ever buy a Range Rover with a fault unless you are prepared for and understand the potential cost, time and frustration involved in repairing it!