I am planning on remodeling and re-tiling my bathroom. My question is- do I gut the whole space and put up all new dry wall (green board) or keep the the existing dry wall and deal with patching and spackling?
My vote is to patch and spackle as much as you can. Why make more work for your self than you need to. If you have sections of drywall with water damage of mold those should be cut and replaced. I was able to save the top half on my drywall, replacing the lower 4 feet but that was really more than it needed. It may come dow to a choice between what you think the labor difference is between patching/spackling and taping/mudding new drywall sections together.
If the work is minor--Just new tub and re tiling --and the old drywall is in good shape--Leave it.
If you are adding a new fan/light--new switch boxes --moving sink drains-and insulation--
Total gut--patches are hard to make perfectly--the lighting in a bathroom tends to cast long shadows on the walls---
I tend to re-drywall most bathrooms. Ends up faster for me.----Mike---