I probably shouldn't comment here because I home school my children and so we go whenever we want to and don't have to worry about them missing something at school. But I'll put my 2 cents in anyway.
My observation is that we tend to remember that "Dad wasn't at the first soccer game" and "Uncle John didn't make it to my birthday party", etc. What no one can seem to remember is what was so important that kept these people away from important family events! My point is this. You and your daughters will not remember what it was that went on at school the week they would have been on vacation with you. If you go, they have the opportunity to create life long memories of wonderful family moments. Will an extra week out of school mean that your dd's grow up to be horrible people? No. Will it mean you may have the chance to have some quality family time? Absolutely.
As for the message you're sending them, instead of viewing it as a message of poor work ethic, couldn't it also be viewed as a message of "family first"?
Of course if your dd's are failing in school, then taking them out is probably a bad idea. Too many days out really could have negative long-term consequences.
I just suggest that you look at how you believe your decision will be viewed over the long term, and make it accordingly. ("Do you remember the year we took TWO weeks off school to go to WDW???")
Best of luck and God bless you.