I generally use the tool that is handy and simplest to use. I'm not always in Terminal (thankfully) and I have often used TextEdit to create/edit scripts. It works for me, but I also recognise the features of TextWrangler and use it as well. I was somewhat disappointed when it went to the Apple store and the download from there broke authenticated saves, so I went back to Text Edit for a while. The current version of TextWrangler works well though.
I'm not sure what the point of the whole "do this. don't do that." thing is here. Use the tool that works for you. If it fails, try a different tool.
By the way, vi/vim are a pain if you just want to write simple scripts. I recognize the additional features as potentially awesome (if you can find how to use them) but for simple scripting it really is over kill. Time would tell, naturally, whether commiting to vi/vim would pay off for every/any individual scripter.
There is another command line text editing tool available that is a bit friendlier and way simpler. nano. Give it a try if you haven't. You may find it is the gateway drug that pushes your to vi/vim. 😉