As with any type of Pass, do the math.
it will depend on WHAT you want to see. dont forget that they have Opening AND Closing times, so no matter what, they will close before you do.
Also, youre not flying solo, so if your friends dont like your itinerary, its not going to happen, or your going it alone. You may want to make this up as a group so there arent any surprises once you get there. Work out the bugs now and ALL agree to it.
I bought and used the Paris Museum Pass when i was there since it worked out for me. there wasnt alot of $$$ benefit, but where i saw and found the most was being able to pass the entrance lines. Security lines, no, but any line you passup is good.
As far as transit, i bought the pack of 10 carnets. It was the best for what and where i went.
Here is what i experienced when i was there in mid March of 2012.
Since you dont say WHERE you are going in Paris other than the Eiffel tower, i will give you what had the longest lines or issues.
Louve. I entered thru the underground. There was only 12 people in front of me and i got there 45 minutes before the doors opened. There is a day that the Louve is open late. So if youre there for that day, you could take advantage of that fact to open up the day for something else - hint hint. also, i could spend a whole day there easliy. Dont know about youall, but also think about how much time youre going to give each thing. that will help plan out your days.
Eiffel tower - long lines to get tickets. I had prepuchased my date/time. I got there 15 minutes before my time and they turned me back until 5 minutes before my time. No line to enter, just security. Lines for elevators so just be prepared to stand in line going up AND down. dont drink alot before either since there arent alot of bathrooms and if there are, theres a line for that too.
Musee D Orsay. Longer line there about 50 or so people 1 hour before opening. But it went fast.
this maybe a helpful hint and is what i do to minimize my travel distance and time (to make the most of my time & $$$).
i get a map and plot out what i want to see on the map. I also plot out where im staying so i can get an idea on how far im traveling to the place i want to go. Then i look at the closest tube stations for each thing.
i then look at open/closing times and go to the furtherest thing first and work my way back to the place of stay. that way if i have to go back and forth, im traveling shorter distance each time. I also try not to chris cross over the place to see things, but i try to place things in areas or zones or group them togeather.
you dont have to do this, but for me it helps keeping things straight and minimize my travel time.