Standard 5906 pistols are going to be rare.......someday.....like 20+ years down the road.
But hey, they are great solid guns that will eat anything - including empty cases. Really, empty cases...
The TSW series pistols, on the other hand, have been creeping up in value - even the police trade-ins. Personally, I don't buy 'em for their collectability or their ability to appreciate. I have 'em because they are a dying breed. They're solid stainless steel and are as accurate as many of the custom jobs - for somewhere around 1/4 of the price.