Neovim uses LuaJIT on most distributions (or when building from source), which is substantially faster than Vimscript. Although this only really matters in computation-heavy plugins.

The only other "advantage" is that the Neovim development team is 100% all in on Lua, and Vimscript is essentially in "maintenance mode". We still port patches from Vim, but even Vim has moved on to Vim9script, which Neovim has no plans to support, so traditional Vimscript is very likely not going to see any improvements from either Vim or Neovim.

None that i've seen. Everyone seems to love Lua but its a mess for a config language -- its just untyped dictionaries passed around everwhere. Spelling error in some special string keyword? Too bad.

Might as well use lisp at that point.

Better documentation and support. Since Lua is a well-established language, there's a larger community around it than something like vimscript. What I've heard from the community is that vimscript and its quirks are difficult to deal with, which complicates plugin development. Lua support means more complex and stable plugins, but if you prefer vimscript nobody's stopping you.