snyderprosky, I know the Madrid airport's T4 very well, and I agree with CaliMom. Getting from the plane to a train isn't horrible, and in some cases, it's the smartest or only option. In your case, I would definitely try to fly straight from Paris to Barcelona.
If you can change the ticket, even for an added cost, great. I'd even consider throwing away that old ticket and buying a new, one-way from Paris to BCN. (But ONLY do that if that leg is not part of a ticket that will continue with, say, your flights home. Abandoning a leg will cancel all legs after it.)
I'd also add that splitting 5 nights between both cities is undercutting both of them—adding unnecessary travel time only makes that worse. Moving at a rushed pace in Spain may let one see more sights, but it makes it nearly impossible to experience a sense of place. I'd suggest you look at spending 5 nights in Madrid with a day trip to, or even one night in, Toledo.