Ruby, Python, and in the game-dev world, Lua have become quite popular without curly brackets and semicolons. I don't think syntax is all that critical to a language becoming popular[0]. What does matter is that it solves an immediate problem that simply isn't being solved by other languages, or is attached to a framework or tool that does so. Python got popular because it was a more readable replacement for Perl. Ruby got popular because it was used for a framework that eliminated half the work from the average web app[1].

[0] With certain limitations. A painful syntax will keep people away, and it remains to be seen whether Lisp is painful enough to most programmers to prevent adoption when a language otherwise solves all their problems.

[1] Compared to PHP, Java or just about any language with CGI and a hand-rolled data access layer.

Syntax does matter. The lack of expected operator precedence kept many technical non-programmers away from Lisp and Smalltalk. Python, Ruby, and Perl all succeeded because they respected the cultural expectations of *nix hackers. Cultural expectations are a big factor in HID. Programming langs are just a highly specialized case.