Well clojure having a lisp syntax allows an optional type system to be build as a library.
Or use an existing, language provided parser - haskell-src-exts, for instance.
"it would need to be a extra step in your compilation pipeline"
I don't see what that has to do with syntax. Any compiler could have a hook where it hands off a parsed AST - many do.
I have jet to see compiler hooks that are as simple as to write as they are in lisp. Also, most of them are far less powerful then they are in clojure.
I see tons and tons of example were people use clojure macros in intressting ways but not that many people who write scala compiler hooks.
So in theroy you are right, in practice I have not jet seen tons of examples.
Clojure has a lot of great things going for it. I don't have any objection to Lisp syntax - I like it although I don't know that I prefer it - but I don't think we should be crediting it with things more properly deserved by other pieces. Proper support for macros is a biggie.
It has to do with the syntax. Working Lisp "plugins" is very simple because all the code is represented as plain datastructures. Rewriting program is like writing simple data structures manipulation code.
Strictly speaking, AST data structures are often full of junk, but that's not mostly a matter of the complexity of the syntax itself but of the variety of things being done with that AST - you can't report error locations if all you have is the nested lists representing your Lisp program.
The focus on making macros work well is absolutely a strength of Lisps. The syntax is a much smaller part of that than the lore would suggest.
More syntax makes things harder, compiler that have not been designed wit this goal make things harder. You can look at the papers trying to get this stuff in to other langauges and there are some problems, dylan [1] was doing it befor most others, now rust is coping that stuff.
Actually some of the coolest stuff was done by David Moon (Common Lisp, Dylan) he greated a langauge spec that he calls PLOT [2] and it has a very inovate macro system. For anybody that is intrested in that sort of stuff I highly recommand it.
[1] http://people.csail.mit.edu/jrb/Projects/dexprs.pdf [2] http://users.rcn.com/david-moon/PLOT/ and http://users.rcn.com/david-moon/PLOT/Moon-ILC09.pdf