Hi Andy,
I have had a couple of these 3.50″ rims pass through my hands and have seen quite a few and can attest that they are all exactly the same as the standard 3.00″ rims apart from that
extra Half Inch of course. So the “Silver Rim” theory is a bit of misguided sales BullShiiiite. I would say the anodising has been been worn/abraded off by some means.
As for Value… I currently have a 3.50″rim on my RD and this is an advantage if you want to fit wider tyres to the rim. Anything over 130mm wide on the rear tyre is actually out of
spec fitted on a 3.00″ rim as it changes the geometry of the tyre significantly. I’ve seen tyres as wide as 160/80 squeezed onto a standard rim which makes the tyre seriously
unpredictable on the edges. OK for motorways though I guess.
The widest tyre I have found that would be in specification on a 3.50″ rim is a 150/70. I have a set of radial Bridgstone 150/70 on my RD and gave them a serious scubbing around
Castle Donnington in April. They are the best tyres EVER for an 1100R, the only downside is I’ve seriously scrapped the footpegs getting the bike over on the edge of the tyres around McLeans and Coppice:rolleyes:
Now the problem… you can’t get these tyres any more in an 18 inch. So when I’ve shot these I’ll be back on BT45’s.
So value.. well as AndyJ says as a novelty you will pay the premium over a standard wheel and you don’t see them offered for sale often. Thing is, apart from the novelty will you get
any extra value yourself. If you can get the extra performance out of wider tyres, ie. on a racetrack, then it’s worth paying more than a standard wheel. Basically, could you use an extra Half Inch Andy ?? 
If for show and the novelty factor then for the afficionados the wheel is effectively damaged so what do you take off the value for that?
I guess there’s not precident for how much to offer on these so it’s over to you and your wallet then !