seems pointless to me paying the guts of a quarter of your liability to get someone to tell you what should be reasonably obvious, also will they be liable should Revenue come up with a challenge?
If I were a valuer I'd be adding a caveat to my valuation that would ensure I cannot be sued in case of Revenue contesting the value entered for the LPT.
If houses in an area aren't selling how will the valuer come up with a reliable value? If they are selling, the Property Price Register will tell you what they're selling for.