From a practical standpoint, no. Machineguns are not worth it. A machine gun will do you no good whatsoever for self defense, defense of a dwelling, or just about any scenario I could imagine, short of a civil war. Hunting with a machine gun isn't permitted, but even if it was, that would be absurd.
And, what the heck are you going to do with a registered
machine gun if you ever find yourself in a position of having to do battle in a civil war, or against a tyrant that has taken over your country? In a true SHTF scenario, no one is going to give a crap if you happen to have a Form 4 with a pretty looking stamp and your picture pasted to it. If you use it to fight your own country, waiving around a Form 4 isn't going to keep you from getting shot or imprisoned if you aren't successful.
From an investing standpoint, machineguns are worth it based on historical prices. Unless there's another amnesty (which I don't see happening), supply can only get smaller and with population increasing, demand will get larger. Super rich people might pay hundreds of thousands of dollars to be the only "cool" kid in their exclusive neighborhood who has a machine gun. Who knows, Uber-rich folks have paid millions of dollars for ugly paintings. Machine guns are prettier, cooler, more "adventuresome", funner and more impressive than an ugly painting.
From a "fun" standpoint, machineguns are not worth it unless you have so much money you don't know what to do with it. I paid $2,400 for my AC556 when I bought it - I would never pay $6,000+ for one today, and I sure as heck wouldn't pay $13,000+ for an M16!! They just ain't THAT
much fun to shoot. For $15,000 I could get a V8 motorcycle with unlimited acceleration and power at the twist of a throtle.....now THAT'S
what I call 15K worth of fun!!!!