Two suggestions:

1 - syntax highlighting in the internal script editor.
2 - getting rid of the whitespace dependencies; Using a simple syntax stack for parentheses, brackets and position within a script would solve the whole need for whitepacing things like 'if', 'while' and {} blocks "properly".

An additional suggestion which is just blatantly a feature rather than something that is (imo) functionally desired, is a scriptstack window. Something like the remote section, only with a pulldown menu of all scripts currently loaded, so that they can be edited and reloaded from within mIRC's editor. This would of course only really be functional if syntax highlighting would be implemented, otherwise you're just looking at pages and pages of uniformly coloured code.