Refits don't seem to net you any return on the old components which are refit. I have not tracked this explicitly but at the moment the NCN is in a major refit phase and for some ships I certainly have seen that it is often just as effective (and more so from a mineral cost point of view) to scrap and rebuild rather than refit.
The two reasons to refit for a ship undergoing major changes are that you retain a trained crew if you refit, and you have to retrain them if you scrap and rebuild. The second is that refit is also considerably faster than the scarp-rebuild route.
I can take a look the costs and see if I can spot any re-imbursment going on but I am dubious it is. I know for example that a refit that changes the engines costs the full cost of the new engines, it was one of the reasons that due to the Gallacite shortage that stopped refits and upgrades and even new builds. Since the NCC has gotten a steady trickle of gallicite going things are back to a modest level of building and or refitting.
