How do nim users who have some proficiency in Lisp compare the two?
I made an inquiry on r/Lisp and it didn't go down well, and it seems Lisp users are quite happy with their language
Are there any Lisp developers here who have used both in earnest?
Really the only thing that Nim and Lisp have in common is very powerful metaprogramming. Aside from that - it's a very strange comparison...
Lisp is a family of programming languages, almost all of which are scripting languages without static typing. Most common Lisp implementations (ex. SBCL, and some might count Clojure) cannot produce lean high-performance executables, which is a big strength for Nim. Kostya's benchmarks show Nim being much more efficient than Lisp variants Racket and Chez Scheme.
Lisp is especially known for its peculiar S-expression syntax, which now (adding up all Lisp and Scheme flavors) has less than 1% market share. A small minority of programmers like it, but the vast majority don't, and would probably find it difficult to read your code or contribute to your project. Nim's syntax philosophy is shared with Python (soon to become undisputed as the most popular scripting language), and so it's less peculiar than Lisp to people coming from other top programming languages.
Related: Make a Lisp in Nim (2015)
There are a few lispers around. One of the biggest is @kaushalmodi. He is often on irc. I would ask him there. He has a great Nim notes page here: https://scripter.co/notes/nim/ (His entire website is generated from an org-mode file I believe)
I am a novice at lisp but I have played with a few flavors. Nim macros have a similar feel in some ways, but very different in others.
Just like lisp, macros essentially act as functions over the AST. But, Nim is a strongly typed imperative language, and as such, the AST nodes that you are operating on are much more "rich" to accommodate this. It's not just lists all the way down. It feels more like building a small plugin to a traditional compiler. Personally, I find writing macros in Nim to be more similar to building a DSL in Haskell, or ML.