Both plates are limited in number and hence in tight supply, which is what's driving the price up even higher than the price of car plates. Shanghaifingers recently posted about a conversation he had with some big ganbu in the Vehicle Management Bureau, who said the status quo will continue for some time -- no new plates into the supply, and a level of official comfort with the high secondary market price of plates. It's crazy to spend more on a plate than on the bike itself, but the system is mature and transparent and no one I know has had any problems with transfer of plates, either on an existing bike or stripped off a bike that's being scrapped after its 11-year legal lifespan. No investment is without risk, but with the current policies it's hard to imagine a plate dropping in value. Remember, a bike plate can be transferred to a car, thus reducing the overall supply of bikes and boosting demand and price, while a car plate cannot be transferred to a bike. It's hard to see the downside of buying a legal plate, other than the deep, deep hole in your pocket.

Of course that is not investment advice, and your mileage may vary!!!

cheers!