I wish ED's Engineering took a page from games like Monster Hunter World. In that game, when you upgrade a weapon, you can later "undo" a particular upgrade and your materials are refunded to you.
My second CMDR just bought a Cutter - the first Cutter I've ever owned after 1.5 years playing the game, woot woot! I can't afford to A-rate the things I typically would, so I'm settling for C & D for now. Because the jump range is rubbish (thank the Guardians for that booster), I'll likely G5 my 7C FSD. Some of those "materials" are a big pain in the stern to gather, so it sure would be mighty nice if I could get those mats & data crystals back to use on my 7A FSD when I can afford it.
BTW, I inadvertently shine a light on another problem with Engineering. In many cases it's optional - nobody needs a ship with 80LY jump range or lasers than can melt an NPC in 2 seconds. However, take a ship like the Cutter, and without some serious engineering, it's just not that fun to fly (that's including the very sad default jump range). Nine times out of ten, I'm engineering to compensate for weaknesses in things like weapons range, FSD range, top speed, etc. Nothing I have is a "god ship" (no 80LY JRS, no 800+ m/s thrusters, no instakill phase-shifting quantum entangled bacon-powered torpedoes). Nope, I just want to the ships I like to be good, not necessarily super. That makes Engineering mandatory, whether I like it or not.