First off thank you for Script Workspace - its great. When I go back to versions before version 14 and edit a script, I always have to pause a moment to realize that I have to choose each step. Huge timesaver.
Variable use - have I declared a variable that I haven't used yet, and have I used a variable that I haven't declared
More color choice options
Find and replace, or just even find for that matter
Improving the Script Workspace could also add improvements to the debugger. Things like enter debugger when this condition is met or a list of all the errors that a script has encountered during its execution.
Built in way to for parameter passing. I know its been mentioned... but this would also be a huge timesaver when writing scripts.