Val, the issue is with the poly bushes which due to their design will automatically increase NVH...and I'd imagine this would be quite an NVH/.jarring increase in a Landy. I've poly bushed many cars over the years knowing what they can do to ride quality et al, and often do not install them where I think max' NVH will be transferred into the cabin and/or cause "crashiness" within the car's body/chassis. This means some bushes are poly, some are left std OEM and for road use this is the best way of suspension upgrade. I'm in the process of upgrading my suspension on the D90. I've thought long and hard about poly or rubber bushes. I'm going with OEM rubber bushes except for the panhard rod. My reasons are 1. Defenders are not designed to be circuit racers, and 2. studying the LR axles, the greatest improvement is +Ve axle location to allow the panhard rod to do what it was designed to...providing the correct poly bush grade [shore rating] is used, 3. with suspension joints now new, the coils springs and dampers can be spec'd correctly spec'd [matched] to give the ride you want. {possibly progressive springs and adjustable dampers...or go std set up - there's nothing wrong in the way a Landy drives providing the suspension is looked after, regularly greased and set up properly.
Adjustable dampers may improve the 'softness' of your ride but will not remove the excess NVH from your Landy and will reduce the road holding too. Why not replace the poly bushes with good grade OEM bushes, then set up the suspension damping to your preferred driving style...