Yeap, you guessed it, I had to bite.
Anyway, you're forgetting something, and that is that the public who pays a railway preservation groups bills doesn't care. They don't care that such and such carriage had a different window arrangement to its sister or that loco whatever was the only one to be painted green. Only railway enthusiasts like you and me care about that crap, but it's not us that's paying the bills, far from it.
The public spend on heritage is getting smaller and smaller so being a bit smarter is the key. Why spend huge amounts buying and restoring DP13 when all the public needs to know is that they're riding in DP14 which is much the same, and that DP13, the last passenger railcar in Tasmania is now restored and up in Queensland (you can even print that on a pamphlet!). The public won't care they didn't ride in DP13, all they'll care about is that they went for a ride in an old train.
Nobody except for a few gunzels care about small rivet details, and that's one of the downfalls of railway preservation. Gunzels would rather keep the first and last of everything as well as the one in between which was painted red back in the day instead of limiting their scope and picking the best example. Instead of being happy with one and maintaing it in first class condition, they'd rather have five with four of those rotting out in the rain because they think the public cares as much about light fittings and an extra window as they do.
Tasmania doesn't have the people, money or time to take on the restoration of DP13 when there's other near identical cars already operating. Buying and trying to restore DP13 because it was the last at the expense of something like a steam locomotive's overhaul (a real public draw card) is just ludicrous gunzel thinking.
As for DTT, I really do commend them on what they're doing and wish them all the best. In saying that though, they should probably stick with the diesels and achieving something there instead of grabbing a burnt out railcar that'll be detrimental to their efforts and the restoration of their main project, ZC2144.