When do you need a Website Redesign?

I ran across this funny post.

Seeing this made me think of the websites that are abandoned each day, each quarter, by businesses that decide they need to redesign instead of enduring the less glamorous process of website optimization.

It can be difficult to decide when a complete web design redo is needed and when you just need some subtle changes.  For larger companies, this can be decided by their sales goals and what new products are coming out.  For smaller companies, it’s usually an issue of cost.

How much do you have set aside for a redesign?

Will it translate into more sales?  Are your conversions very low?

Has your competition changed their website recently?  Do you need to keep up?

Of course there are the tech questions also such as how it was originally designed and how much you can alter on the fly.