I am by no means an expert on ANYTHING french, or Paris or DLP.....
We went to PARIS for 5 days on my DH business trip and we onlywent to the DTD part of DLP. We went in a couple shops and got some gifts and ate dinner.
BUT.........the ride on the metro, was about 45 minutes late in the evening.
So i would suggest, staying in Paris and going out to DLP for the day.
The metro system was very easy to use even for me, who has never used one before even in the states.
JUSt decide what you want to do and enjoy.
I went to montparnasee and had a lovely lunch on my own while Dh was at work, BUT i think the one thing i did that was a not to miss, is NOTRE DAME...OMG!
OUR goal is to go back for a month in about 4 years when we an take our children and they will be old enough to enjoy and understand.
ENJOY YOUR TRIP!