Those with lots of money will almost always have lots of money. The credit crunch won't affect them that don't need credit. It will affect the ordinary man more, with mortgage, car loan and credit cards etc.
Back on topic:- Certain armoured vehicles and particularly world war 2 ones are seen purely as an investment by some people, no interest in running and maintaning a vehicle happy for it to sit somewhere and accumulate value. And in these times of other investments looking decidely dodgy I can only see the clamour for armour getting worse.
Maybe it's following the same pattern as classic cars did a while back (these are now resurgent as well) and eventually the bottom will fall out of the market, when everyone decides there's more to be made on the stock market again.
I don't think tanks are seen as high fashion. I don't see pop stars or footballers driving them round Cheshire or even taking them to military shows. They'll just be layed up in storage somewhere for no-one to see. :-(