www.emovieposter.com have a very useful searchable auction history, if you search and filter on Japanese B1, that should help with rough figures for value.
You can't look at it in an across-the-board way. Some areas are way up, some way down, some holding steady, etc.
The biggest trend I see is the same it always was, that while true classics of any era generally hold strong, lesser older material tends to decline. You see this most strongly in things like 1940s B-Westerns (people like Eddie Dean or Whip Wilson), where there are almost no people alive who even remember them, and the posters are photographic and uninspiring.
And of course some areas keep defying the naysayers and rise more and more. Just a year after most collectors were shocked by a Jaws one-sheet selling for $1,000, one goes for $3,700 (but admittedly it was rolled and just about perfect). Will it be a $10,000 poster one day?
But here is what I see as the biggest change. Many years ago, it was hard to find ANY old movie paper, so people would "settle" for lesser items (both in terms of content and condition), because they often couldn't find much else.
But NOW, there is so much material out there (obviously at auction, but also from dealers the world over) that hardly anyone sees any reason to settle for a lesser item, when they can surely find something else they want more, and in just a matter of days.
So I am seeing lots of items selling for just a few dollars each that might have sold for much more ten years back. But of course remember that asking prices don't equate to selling prices. Just because dealers were asking $20 each for lots of items that now sell for $1 to $5 each doesn't mean hardly any were ever really selling at $20.
And on the other end, I have never seen a stronger time for top items in nice condition. Looking at recent results it is clear that collectors are willing to go the extra mile and pay record prices for exactly the right items.
