I imagine 20 years from now the gun you buy today will be possibly worth 2 times what you paid for it today.
Considering cars yes they depreciate really bad for years but then some later on are worth over 10 times their original price. Oh how I wish I could buy a 1970 Z-28 for $3000 today.
Look at the increase in price of guns since even 2000. Yeah I wish I could have bought my Python for $400. I have several guns that right now I could sell for double what I paid for them back in the 90's.