I second, third, and fourth what others have said. Variety is the spice of life, and the AK has influenced/played one of - if not the - biggest roles in modern firearms development. If you're an AR nut, they make AKs in 5.56. 7.62x39 is cheap - 20 cents per round shipped or even better if you're shrewd with sales. 5.45x39 gives 5.56 a run for its money and some say even wins that race, if you want to stick with a speedy 22-caliber round over the squattier 7.62.
My first AK was a WASR-10. Still have it, still probably my favorite AK just because it's cheap, loves abuse, and runs like a top. I now have more than 15 of them from half a dozen countries. I find them intriguing, unique, historic, easy to use, stubbornly reliable, accurate ... the list goes on and on. Also, it always makes me smile when I show up at the range and pull out a few grimy Kalashnikovs when everybody else there (and many times, their mothers too) is shooting the exact same black rifle. In my humble opinion, AKs simply have way more character.
Honestly, I can't think of a reason not to have (at least) one AK. And I do own two ARs.