Allow me to bare my soul.
In 2008, after starting and growing a successful web agency for eleven years in the nonprofit and advocacy space, I realized something that nobody in the web agency world wants to own up to:
Quite often, website redesigns are not very good for the client
They over-promise, under-deliver, run over budget and over schedule, and don't actually improve the performance of the client website because nobody bothers to measure the website's performance to begin with. They are often sold to boards and executive directors as ways to get more donations and volunteers, but nobody actually computes the return on investment of the dollars spent in a website redesign because the results are awful.
What they are is often an indulgence in new graphics and a new content management system, neither of which are likely to improve the results of the site in dollars and volunteers.
This is not something a lot of agencies want to admit because website redesigns are the largest engagement (by dollar) that an agency does with a client. And this brings me to my second secret:
Website redesigns can often break the effectiveness of your online marketing
in ways that you and your agency probably aren't expecting.
If you look at your analytics data, you'll see that you get a significant amount of traffic from organic search and link traffic. Whether you have a formal search engine optimization (SEO) program or not, you're getting a notable amount of traffic from Google and from people who link to you. That traffic most likely does what you ask (gives money, signs up for lists, etc) more often than any other traffic.
Website redesigns alter things like page layout (which affect search engine rank and conversion rates), page file names (which affect search engine rank and in-bound links), and content (which affects search engine rank and conversion rates).
It is nearly impossible to do a website redesign without changing these things, and I've seen them degrade the effectiveness of a website more often than improve it, though the websites always look prettier when the project is done.
This e-book will give you some guidelines for things to watch out for in your redesign. It will either tell you directly what you should and shouldn't do, or tell you how to measure the impact so that if the redesign degrades something important you'll know its happening and be able to react.