Since I switched to nvi I've learned way more about the powerful features of the base editor as well as shell tools like grep, fzf, fmt, column, wc, expand, pdftotext, pandoc, make, git... With tmux I have easy access to any REPLs and man pages I need. The main feature of nvi I need over the original vi is unlimited undo, though ex command history and file name completion are nice as well.
Part of the inspiration for me to switch from vim (and spacemacs) down to nvi was this post on stack overflow [1]. When I really grokked the power of this system I picked up O'Reilly's book on vi and vim [2] and read every page of the vi and ex stuff. There is soooooo much you can do with this editor that doesn't require plugins yet people reinvent them, often in a less powerful/flexible way.
Since learning to be productive in nvi, it's going to be very hard to go back to those bigger, more extensible editors. The temptation for bikeshedding is too great... Oh, and learning to read code with syntax highlighting turned off is really nice. It helps you write more clearly since you aren't relying on the highlighting to help the reader.
[0] https://sites.google.com/a/bostic.com/keithbostic/vi/
[1] https://stackoverflow.com/questions/1218390/what-is-your-mos...
[2] https://shop.oreilly.com/product/mobile/9780596529833.do
http://blog.carbonfive.com/2011/10/17/vim-text-objects-the-d...
Ironically I think most of the IDE (ie intellij etc) vim plugins have them while you do not.
Code completion, like syntax highlighting, seems to be one of those tools that changes how you think and I'm not sure it's for the better. Being able to quickly bang out a bunch of glue code may be great for a 9-5 but I think it gets in the way of the creative process. That's just my opinion, though. I'm not aware of any research into this idea.
However I've recently started from scratch with Vim 8.0 so that I could try out the new packaging features that are built in. I also wanted to be able to use the same configuration across Windows and Linux, which I'd found difficult with some package managers.
I've been pretty happy with the result so far. There are still some things that don't work correctly on Windows (shell incompatibilities in plugins mostly), but for the most part it's my IDE now.
One thing I will say for distributions is that it is a great source of new plugins that I haven't heard of or considered before.
A community configuration like Spacemacs will continually update to provide you with a configuration that is up to date and doesn't break.
As far as I understand, it currently does not do that, since elpa/melpa/... packages are updated out of sync with Spacemacs and the last Spacemacs release is over 2 months old. See:
https://github.com/syl20bnr/spacemacs/issues/2057#issuecomme...
But, there is hope, the release notes for 0.200 say:
For 0.201 we plan to introduce stable snapshots of elpa repositories, a new installation of Spacemacs will always install packages from this stable source.
If I may suggest - have you considered adding it to the Awesome List either at:
https://github.com/sindresorhus/awesome OR https://github.com/mhinz/vim-galore ?
So I put to the repository only .vimrc and an short shell script install.sh that installs Vundle, .vimrc, and then installs all the plugins by running "PluginInstall" command in vim. Installation becomes just cloning the repo and running install.sh from it.
The additional benefit in comparison to say putting plugins to git submodules is that I don't have to keep my vim repository at GitHub up-to-date with latest plugins versions because Vundle anyway installs the freshest versions.
That's sort of why I recommend Vim as an IDE[1] to people. It teaches people how to configure Vim for themselves, so they can better understand how the pieces come together.
[1]: https://github.com/jez/vim-as-an-ide