[exmadscientist]

This is the right answer.

Major redesigns to marketing pieces (aka, advertisements) are fine. No one spends a long time staring at them anyway.

Major redesigns to tools will annoy the hell out of their users, unless things are done very carefully indeed (or the old tool was indisputably awful). You've got to look at how novices onboard to and use them, how intermediate users use them, how experts use them, and, if you can find one, how a master uses the tool. (The master will probably do something that surprises you. Make sure your redesign does not piss the master off, unless you like firefighting.) That's a lot of work!

Unfortunately, most things in life are tools by this definition, or at least close enough to them.