I'm not Catholic, so I'm not sure of the specific importance of special days like Christmas (Jesus' birthday) or Easter (Resurrection Day) as far as special worship services. I'd also be curious to know if the population of Catholics in general in the USA has gone down due to all the bad publicity regarding the child molesting priests and the seemingly apathetic stance taken by the Papacy.
My views on the Christian religion in general involving attendance are as follows. I'm in Kentucky, so I think this will be pretty accurate for the South and for other rural areas around the country.
There are 2 types of churches now. Churches that are dynamic, singing contemporary songs, having alternative worship styles (like drums, guitars, bass, dance, etc.) that are growing, and churches that are dying, made up of folks who are mostly 40 and above and want to do everything like they did it in the past. That said, the churches around here that are dynamic have more attendance than ever before. The second type are poorly attended and well off their traditional attendance highs.
Now, being dynamic does not mean that u have to change your doctrine or what u stand for, I wanted to make that clear. So, in answer, I think it depends on what type of church u attend. Personally, we have more than we ever had. I would guess that the Catholic, Lutheran, Episcopal, and possibly Methodist churches are down in numbers secondary to the traditional, ritualistic, non-dynamic nature of the services (I'm not dogging somebody's religion here, just stating my observances).