restuffing a sleeping bag

Most (if not all) synthetic bags aren't baffled so before you could restuff the bag with high quality down you'd have to add them. The stitch lines on synthetic bags are typically there to stabilize the synthetic insulation and keep it from tearing apart, thus developing cold spots. Adding baffles and then stuffing the bag might be more trouble than it's worth because you'd basically have to tear the bag completely apart, add the baffles, then the down. On the other hand since you already have the material and you like it, it's definitely cheaper than buying a new bag or purchasing the materials from scratch. Guess you just have to decide if all the effort is worth it to you.
(Although I've never heard of a baffled synthetic bag, I could be wrong so maybe your bag actually does have proper baffles, although I doubt it, rather than the normal stich stabilization and/or shingle construction. )

bobby c,
Ryan has good advice there; you would have to install baffels. Even if you like the shell material, it may have so many stitch holes after you remove the quilting stitches that it will shed down badly.
However, you might consider removing the old polyester insulation and installing something good like Climashield from Thruhiker or 3D from Outdoor Wilderness Fabrics. Either one can be edge stabilized (along the seams joining the 2 shell halves) and spot quilted by hand every foot or so. See any of the many posts on making synthetic quilts for details. Both Climashield and 3D perform nearly as well as down, although no synthetic is as comfortable as down when the temperature gets up a little.

ahhh yes, i assumed those were baffles and they're just a bit of stitching in the synthetic. well, quilt it is then. i don't think i can satisfy my need for a good bag unless i try to make one myself. i've talked myself into and out of every bag in the degree range and price i want and it's either buy one to just get by, or wait and buy the one i want, or make the one i want. i have access to an excellent seamstress, and all she charges is beer, so that quilt is looking better and better.