Agree with Red C220, if you're hearing clunks, the components of the suspension that give you the smooth ride have failed.
Bushes that fail enough to make a noise should show visible deterioration, so it's worth having a good look at all the "moving bits" underneath.
Shock absorbers (dampers) rarely give away anything visually, unless they are leaking, but you can be sure at that mileage they're worth changing.
Euro Car Parts have some good deals at the moment, you don't have to go OEM to get a good ride.
All the above being said, you need to assure yourself thet the viano has an acceptible ride (to you) in the first place. Get a ride in another one (preferrably lower mileage) and see if there's a difference.
If it's roughly the same, you may need to consider something else....