1) Lengthening the swingarm for your application is a performance down grade.
Application was mentioned? I missed it
2) Lengthening the stock tubes on any swingarm will make it significantly more flexible, Doesn't matter who does it, what technique they use, how expert they are or how awesome there skill level is. Whether or not this is important depends on the application. It is not hard to do safely.
I disagree, your cred just dropped a notch. see image.
3) Lengthening the swing arm obviously lengthens the wheel base. Longer vehicles are less nimble.
What a Drag :
4) If the improved appearance or stance of your bike is worth the functional trade offs to you, then it is a good idea. Personally, I prefer good looking girls, I don't care if they can't cook - I can navigate the kitchen without assistance!
I like a super sexy chef in da kitchen :-*