I never did it myself, but I think you might be able to change personalize the CSS in your "Personal Nodelet" (?) to enlarge the box.

Maybe try Super Search for "CSS", "Personal Nodelet" and "textarea", I'm sure it's not a new topic.

Good luck and please tell me if you have success!

UPDATE:

• In Display Settings you can add your personal CSS!
• OK, trickier than I thought, but this works (at least in my FF) limiting the size exclusively to the "new question area" textarea[name="perlquestion_doctext"] {width:600px;height:300px;}

  for more ideas look at PerlMonks CSS Examples

  ---

  In reply to CSS for textarea of new question by LanX
  in thread How can one enlarge the "Your question box"? by szabgab

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