Personally I don't feel the anything will be achieved by blocking off the EGR valves. Experts designed these rather good engines, and it is the government + climate control regulations the has introduced EGR Valves, DPFs, and other additions to the exhaust systems.
Not being a design engineer I tend to go along with the principle that I should manage my car in the condition it left the factory. [mine left the production line in Castle Bromwich on 13th March 2007, and only the Leaping Jaguar on the bonnet is what is different.
The engine is the same - no remapping or similar "improvements" -- the exhaust will last as long as the car being of stainless steel and I guess the car will last as long as me. [I am now heading towards my 85th Birthday.]
The cost of maintenance of a Jaguar is not that high if you look towards preventing problems rather than fixing them after the event.
My recommendation is Premium fuel and the odd additive. Changing the oil when it needs doing. Checking the tyres, the battery, and the engine fluids.
But that's just me. I have a degree in nitpicking but it does seem to work.