You are missing some info that would allow us to help.
Are you going alone? Are you looking for female companionship?
Assume so, but you did not say - if you want good advice, be as up front as possible in your post(s) - most will be happy to help
If you are looking for hook up with some, er, hookers, its not the greatest time in the world to go - you sound like a newbi (nothing wrong with that - but if you were not a newbi, you might already know its a time period that has some problems), and figuring it out is tough enough the first few trips without the hassle of being there at a "difficult" time.
Fact is MANY - NOT ALL girls are spending time with their family during the Christmas to New Years time period. A few days after New Years Day, the place starts to get back to normal.
I don't think they all will be, so you can probably find some companionship - overall, along with Easter Week, its not a time period I'd choose, especially if I was new to Costa Rica.
You have many more options for girls in San Jose vs Jaco, although some lately are posting about Jaco like it the "new Rome" - I know better
Others can better advise you on Colombia.