But still, it's a bit of a gamble depending on how you look at it. Supply is fixed and falling. There will not be any more lenses or cameras made, cameras will break and lenses will go mouldy, no new ones are coming onto market. But what about Demand? Either it will fall (people are selling their big old clunkers and buying the latest 35mm lenses for digital), or it will rise (collectors move in, hoping to score something nice for the cabinet, for the grandkids to sell to fund their way to college). Which one? No idea.
My observations in general have been that prices are rising, or at least have risen a lot in the last 10 years, for a lot of 35mm gear. I've heard of people here getting soviet junk almost for free 10 years ago, I read yesterday someone bought a decent condition kiev rangefinder with Jupiter 3 50/1.5 for $20 a few years ago. I saw a Jupiter 3 50/1.5 sell yesterday on fleabay for $150!
But that's 35mm, and a lot of those lenses are being adapted to NEX and other mirrorless, especially wide-angle and fast primes, so that explains them going up a bit.
Still, in MF the lens prices are gradually going up too, I regularly see CZJ Pentacon6 gear going for over $200 for the rarer MC 50/4, 120/2.8, 180/2.8, whereas I bought my set of those for maybe $100 a piece only a year or two ago.
Long story short, if I had the cash I'd be investing in some good hassy glass if you can find it cheap and second hand.