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. )