It is worth that much, if I wanted one i'd buy it and change to a V8. If it was a HQ it'd probably pull $15k.
Just before I bought my Premier I offered $10k for a one owner 6cyl 4spd red WB Kingswood ute, with. integrated air, U17 dash, buckets and heavy duty radiator. It had about 80,000kM on it. This was maybe 4-5 years ago, he got $12k for it. Plan was to put a whole blue 4.2L in it with all as per original bits, change the input shaft to a V8 one on the M20 and stick a Salisbury diff and V8 tailshaft in. Body and paint and interior were mint, just needed the RH quarter bump strip changed as he'd used a gutter bolt to fix it back on when the front clip broke.