museum pass

It depends on how many places you intend to visit over 5-6 days and how the cost of individual tickets stack up against the cost of the pass, then weight in the convenience. However, remember no one can skip the security line. Passes can be bought for 2, 4 or 6 consecutive days.

We can't answer that without knowing which sites you want to see with the pass. As Carolyn said, the only way to know is to do the math, comparing the total cost of tickets against the price of the pass.

It will be less economic if you want to space out your visits, but generally it's a good deal. The best part is it lets you feel free to stop in at places that you might not otherwise be inclined to pay the entrance fee, even for a very short visit. You can also visit big museums on more than one day to get the most out of the experience, and avoid exhausting yourself by doing it all in one day.

but i want to spread out my visits over 5-6 days

Easy. Buy the 6-day pass. That's what we did for our week in Paris, and had no trouble breaking even on it. As with any pass, you have to do the math: add the total of individual entry fees for the attractions you want to see against the price of the card.

The beauty of the Museum Pass is being able to go back visit the same attraction as many times as you wish to. This was a tremendous bonus for the Louvre: because it's so vast, we covered it (or most of it) over three separate visits including a late-night opening when most other attractions were closed. That alone would have cost us 45 euros if we'd bought individual tickets, and made up a big chunk of a 74-euro pass.

The pass also encourages visits to attractions you might otherwise skip, if budgeting individually. We don't normally buy tourist passes but this one is an exceptional value, IMHO.

Editing to add:
This is how much the 74€ pass saved us against individual fees:

Louvre/Musée Eugène-Delacroix - 45€ (15x3)
Conciergerie- 9€
Saint -Chapelle - 10€
d’Orsay - 12€
Pantheon - 9€
Hôtel des Invalides - 11€
Musée Rodin - 10€
Arc de Triomphe - 12€
Towers of Notre-Dame - 10€
Musée de l’Orangerie - 9€
Musée de Cluny/Moyen Age - 8€

Total - 145€ or 115€ with a single Louvre visit

These weren't the only things we did in Paris but just what we used the passes for. :O)