You have a point, but let's distinguish between optional syntax (like : ' !) and mandatory syntax (as is used copiously in most languages)
Optional syntax has far fewer minuses, I would argue- New users wouldn't need to use it if they prefer not to.
Also, we're not talking about increasing syntax here, just using the existing syntax in a different way.
My personal thinking, though, is that it would be OK to go all out with the other special characters to generate optional syntax, as long as it is really, really, really well thought out. (other arc users, such as yourself, would probably disagree with this argument, however) Some special character for currying (such as described in the current arc.arc comments) would be a strong plus, I think.
the problem is that people will use it. i don't want to read through a:b.c code. my eyes are already optimized for (a (b c)) and i like it thank you very much.