I did sucessfully about 2 years ago. VRT had valued car at 9K for the months I had been considering the import, and their valuation hadn't decreased at all even though throughout that year car prices had plummetted.
I paid the VRt (approx 2.5K), completed the appeal form, with a letter stating the reason for claim (market reality, sample ads for similar cars from carzone etc), outlining why I felt it was 30% overvalued.
I got a letter a few weeks later of acknowledgement, then about 3 months later a cheque for 750 euro or thereabouts - close to the 30% I had suggested.
So if you have a valid case you should get a hearing - takes time though, and you must pay the full amount upfront.