Yes there is probably some window dressing at this time of year,...

Yes there is probably some window dressing at this time of year, however when we come back after new years the market generally plays true to what was going on before the two low volume weeks.

Last year (2014) there was a reversal (shakeout) immediately behind the price before the Christmas/New Year break, then it went up on low volume, and in the new year there was two weeks where price swept lower (the second more violently than the first), then the Index moved higher (possibly in response t0 the initial reversal).
The important points in 2014 are that overall the Index was consolidating after making numerous new highs previously.  It had already pulled back and made a rough double bottom. After the break there was no lower low, just a shallow pullback to check the state of supply.

In 2013 there was also a reversal (shakeout) immediately behind the price, and it went up during the two low volume weeks.  Then price had a five week pullback in the new year, before accelerating higher.
Overall price had made a new high in November, and had pulled back just before the break. In the new year the pull back was effectively a secondary test of the initial pullback, and formed a rough double bottom of sorts. Price then moved higher.

2012 saw the index trending nicely towards the upside, with just a single narrow spread pull back for a week in the new year, then the Index continued on its merry way higher.

And finally in 2011, the Index found itself in that awkward spot two years after the GFC (remember dgorenssons stories.... they were from this point in time).  Overall price was already pulling back before the Christmas/New Years break, and during the low volume break price put in a two bar reversal.  And continued on from that in the New Year in a generally higher fashion, with some false starts & some sideways action, as was going on (and probably necessary) at that time.

...........

So overall price has played with a fairly straight bat after returning from the Christmas/New Year break, and has mostly just continued on doing what it was in the process of doing before the break.

cheers