First one was four years ago, my configuration was rendered completely useless after starting to use OS X and I didn't know where to start, so I forked https://github.com/purcell/emacs.d and rebuilt my config on top of it.
Second one was because every time I take a break from a language like Clojure and Haskell for three months and then get back to it my config for the relevant modes get obsolete. Spacemacs has a big community that continuously adapts language layers to the changes on upstream and provides the best experience for development behind a few flags like "(haskell-enable-ghc-mod-support t)".
After switching to spacemacs my configuration went from 2023 lines of code in the original config I forked + 1005 lines of my own to a .spacemacs.d/init.el file that's 243 lines long (without comments). It provides 90% of stuff I want out of box, and provides many more features I never discovered/configured and most importantly it takes the burden of maintaining stuff I only occasionally use from my hands.
If you are not happy with some stuff fundamental to Spacemacs such as Helm I don't recommend it but otherwise give it a try, it is really easy disable Evil integration if you are used to regular Emacs keybindings.
Spacemacs still leaves a lot to desire. But it's pretty damn close to be the perfect all-in-one text editor I've been looking for.
It was not made for you. If you want to change or automate something, you have the option of either getting Emacs or Vim to do that for you, but only whatever you need.
That's what spacemacs is, in a nutshell. It attempts to marry the keybindings of vim with the technical advantages of emacs (better process handling, server/client setup, etc)
The whole point of Spacemacs is integrating things together around evil-mode in its only little package that's ready to go. If you don't have any interest in evil-mode, then I doubt that Spacemacs is for you.
If you've been using emacs for 20 years and already know how to do stuff and maybe even write your own modes, then it's proooobably not for you. (I mean, you coulda been using evil a long time ago).
The Spacemacs layer setup does restrict you to what it supports, unless you want to do things manually.
it's much more than just viper, but the ultimate goal is the same: to provide emacs with vim keybindings for prefer to want to use emacs that way.