Short answer: Yes. There are tons of benefits.
Long answer:
Security!
As you may know, Android is the most widespread OS of any kind. Therefore it has become the most appealing system to attack. Unfortunately, security leaks often occur and manufacturers fail to deliver timely updates with patches (if any updates at all). Flashing our systems to the newest available version covers these security gaps for a great deal.
Google listens!
The most brilliant developers around these parts and beyond have thought of and implemented functionality that greatly improve user experience. Google keeps a close eye on these developments and perfects these ideas, integrating them into the core of the Android system. Take split-screen mode for example, once just a buggy gimmick and now natively supported in Android N. What once needed much flashing, tinkering with modules and/or build.prop editing, often comes on board on the latest version if proven useful.
Aesthetics!
Since Android 5.0 introduced Material Design in Android, the entire appscape (see what I did there?) has been brushed up matching Google's design standards. Each iteration is a step closer to aesthetic perfection. Animations run smoother, every tap, wipe or pinch reacts more logically, it just keeps looking nicer.
Community power!
Many amazing things are born on XDA. Like Steve Kondik posting his custom ROM – that didn't mean much to him – for the HTC Dream back in 2009 or so. It was praised by thousands and was the start of CyanogenMod. Today his creation, thanks to hundreds of contributors like @varund7726 , can be found on over 50 million phones.
That fresh feeling!
Everything on paper aside, it just feels good to flash that fresh OS version, staring at the latest boot animation for a bit and seeing that brand spankin' new homescreen pop up.
I can probably go on for a while but basically I'm saying we've got a lot to be excited about
