Up until about a year ago, the prices were pretty steady where they were, even for the oldest of the Holiday Barbie, however, these past few months have sparked a rise in sales, and a decline in sales.
This could be for a number a reasons, Barbie isn't as popular as it once was - it's completely out of season at the moment - no anniversary Holiday Barbies are due for release for awhile - take your pick, but the fact of the matter is the prices have had a sharp decline recently.
There are a few exceptions, such as the newest releases still are holding at a nice solid $25 to $50, and the Festival Barbie hasn't budged (but it's rarer then even Platinum release Barbies so it's price really can only increase at this point) but even the 1988, the first Holiday Barbie has dropped dramatically in price.
For people looking to buy, this is a GREAT opportunity to stock up on your collection, grab them while they're low! For sellers, however, this may be a good time to hold on to what you have and see what you can get out of it later if prices change, and they will change I can assure you of that.
As these prices have plummeted, they will again rise at some point. It just has to do with what is 'today's hot topic'. Next year all these prices can spike into new records high, it just depends on the company itself.
I've personally noticed, after collecting for these past many years, that the prices of the Holiday Barbies tend to sky rocket as Christmas approaches and just after it ends (Kind of feels like a 'duh' but sometimes the obvious escapes us all). I also notice the prices go up when an Anniversary doll is due to release. For example, the last Anniversary Holiday Barbie Barbie was the 2008, it was the 20 year release, (and in 2013 it was the 25 year anniversary but it didn't do as well as the 2008 one) so the next one due out will be the 30 year anniversary in 2018.
The 2009 Holiday Barbie was the 50th anniversary of the entire Matell series, the 75th anniversary will therefore be released in 2034 (feels like a long time, I know!) These will be big years for Matell and their Barbie releases and you can almost guarantee you will see people buying their collection releases.
Another way to see what their numbers may look like in the following years you have to see what else they're releasing, which you can do on their main Barbie Collection page, The Black and White series is a big one that they've been doing recently, beautiful Platinum series set that is usually released in the beginning of Summer, I had the opportunity to get my hands on the 3rd one in the series a few years back but they sold out in less than an hour, (and it would have been 10 minutes if they could have stopped the webpage from crashing). Sales were big for all of their Barbies after that one released and people have been looking for the 4th but they haven't announced it yet (they usually do on their collection page BEFORE the Barbie is actually released.
But again, for those looking for get the Barbies for their Holiday collection, best time to stock up! For those looking to sell, if you do than just be aware the prices are low and you may get very little out of them if you're not patient to wait at least until the Holiday season comes around again which is when the prices are most likely to rise, even a little.
Good luck and happy bargain hunting!