Vader- the asymmetry makes him The Bad Guy, when they redid it for the prequels- it was off. Noooooooooooo!
No, it doesn't. Vader force-choking people left and right makes him the bad guy. The only reason symmetrical Vader and TKs feel "off" is because the imagery has been burned into our minds for over 30 years. If they could have made them symmetrical when the movie was made they would have. I wouldn't want a symmetrical TK bucket in my collection either. Even so, I you don't really hear the general tv- & movie-watching, video-games-playing public talking about this.
I noticed in the 300 movie that just came out... Xerses is a symmetrical handsome man, whose gold chain costume is asymmetrical for this purpose. The battle damage on Fett- same deal.
You're comparing machine-controlled assemby-line manufacturing of helmets to what is likely hand-cast and shaped jewelry. And how stupid (and astronomically implausible) would it look if Fett had
symmetrical damage! (The good guys have asymmetrical details in the SW trilogy as well.)
Compare the following:
Scratch-built (balsa, styrene strip and bondo) BSG Viper
Firefly Early pistol, home-cast and all metal.
Serenity Mateba, direct casting of a screen-used
All-metal (well, almost) CNC machined Firefly Vera
Oblivion Pistol (3d printed master, traditional resin casting)
Dredd Lawgiver (same as the Ob pistol)
Proton Pack (cobbled together with accurate parts and a fiberglass shell)
None of these props are "better" than the other just because they happen to have been made with different techniques. As TheBlur said- you use the method that gives the best end result that you are trying to achieve. If your goal is only to test the limits of your scratch-building, by all means go nuts with bondo, clay, styrene strips and whatever. If, on the other hand, you're looking for something close to screen accurate, limiting yourself to certain techniques will make it near-impossible (in any practical sense). There is no practical point in 3d printing a Proton Pack and just he reverse with the Oblivion pistol- to make it as accurate as possible it HAD to be modeled digitally and 3d printed, because the originals were. In each case above the same tools were used- my brain and my hands (except where I bought parts or had help, as with Vera- I didn't machine most of it myself). Sometimes they shaped the object using hand tools and sometimes my hand guided the some form of machine instead be it a computer, a lathe, a dremel or something else. Which one took the least amount of effort? Which was the easiest to make? Which demanded the most amount of skill and knowledge?I honestly don't know- they all have many hundreds of man-hours in them.
To each his own which technique you prefer. They are all equally valid and I wish we could all just accept that. The energy spent debating could be spent making props instead!