In my humble opinion, only you can make that call for what level of detail / perfection your looking for. One thing that goes without question is, by sand blasting with the springs in place, you'll never get all the rust off, and what rust remains will eventually spread back under the new paint.
I disassembled a set on the '66 F100 we restored, blasted them, shot them with epoxy and flattened single stage, then sprayed EZ Slide on the friction areas. Still didn't ride as good as a coil spring sprung '66 C10.
On my 51 Ford F1, I took the spring packs apart, blasted and epoxied (2 coats), then reassembled the packs using poly liners between each spring. As I never drove the truck before I restored it, I couldn't tell you if it makes any difference. Lots of info on the HAMB, if you want to do some light reading.
I've got the rear leaf springs out of Clarence (see avatar) and have another set ready to go in. 1. Based on your experiences should I take this set...