The shellac is just a treatment to turn a newish looking tweed into a vintage look the way they did them backthen. I haven't done mine yet, but in a few weeks I'll take some before and after pics. I believe we use the amber tinted shellac to simulate the aging process.
What value are you worried about losing with a Blues Deluxe? If anything, IMO, you just made the amp more valuable by giving it a vintage look. Plus, you'll never have to clean it much again.