You get a lot more in an SS wagon than just a V8:
-Leather seats
-LSD
-Electric windows
-Traction control
-Body kit
-FE2 Suspension
-Pretty cluster
That's all that comes to mind and of course you get a legendary LS1 is in there ready to rumble.
It would be a good project to swap, but buying an LS1 is about $2-3K. So add that on to the price of the V6. Then think of the problems people have with conversions, it's a BIG job. Do some reading on here, plenty of people have thought of doing it in sedans or done it. See if you want to go through their pain. Particularly the rego situation, whatever it is in WA.
My SS is flawless and I love it, best thing I've ever done. I've got washing machines, surfboards, lounges and push bikes in the back all the time. But I agree, people are charging too much for a 10 year old car. Talk them down, find someone desperate to sell, walk away and see if they come after you the next few days. You could also look at berlina wagons, some of them came out with the V8 if you're not interested in the extra SS stuff. All depends whether you're motivated enough to do a conversion, I know I'd rather just buy it ready to go as a conversion is a lot of work.