Webb gives a great overview of old meters, and details what happens as selenium cells age and go bad. Remember, if you’re relying on an old battery-less meter utilizing selenium cells, make sure you’re either well-aware of how many f-stops it’s off due to age (you can do some simple exposure experiments to figure this out), or you have a reliable and accurate backup meter to reference.
In going against the grain of most collectables, the older models are generally less expensive because their functional accuracy is not as great. This makes vintage light meters an excellent value for collectors not interested in using them for professional photography jobs.
Have at it, eBay speculators!