Like Rob said, if you have the room just keep them all. If you have a hankering for a real Sandman just buy one done already and add it to the collection. Your van in its current condition might pull $4000 if lucky. There are visible rust bubbles in a few bolt on panels and some stains coming from the gutters and seams. Those are the bits that are going to cost if you're paying someone to restore it. Most panel shops aren't interested in rust work and the good restorers have enough work with high end and custom cars that they'll quote prices that would be insane to spend on a van with 6cyl id tags. As a point of reference, a member here recently picked up a genuine 308 Sandman in similar condition (probably better on the rust front as it was a Canberra car) for $6000. If you really want to spend money on something, that's the better way to go.

Even if you aren't doing the panel work yourself you still need a good idea of the process to avoid spending too much money or getting ripped off. Plenty of projects stall due to this and the money spent is never completely recovered. Once you start you need to be committed to the end otherwise you loose interest.
In terms of restoration costs here are a couple of examples I know of recent restorations on Sandman's. First was just under $30k. That was with the owner doing the majority of the work. His son in law was a painter so he got a real good deal on that. Second was in excess of $50k, again with the owners doing most of the tear down and reassembly. Paint done by a good friend at better than retail cost but an extremely top job. Both vehicles were extremely straight and rust free to begin with too. Add in some nasty suprises and it's not hard to add 5k of panel work to the job.