Some of the best reason you should change the design are:
There is always a question what should you put on the homepage of the website. I have redirected my homepage as one of my inner pages where the user can access all of my content and jump to the section he wants. The design of the website should be search engine friendly. Search engine would rank your article on their first page if the SEO is done properly and if those pages have some back links.
If you are changing the design to make it user friendly and search engine friendly than definitely you should do that. It would increase your visitors and boost the time a visitor spends on your site.
I have already mentioned it above but it means that a user is able to look most of the part in the homepage and all the categories are displayed in the navigation menu. Do not make the navigation bar more focused on the drop down menus. It is advisable to display all the relevant categories in which user do not have to hover over them and look out for additional sub-categories (except to the fact if you really have long list and there is a need to sub-categorized it).
If a site is not search engine friendly it is hardly going to find its place in the first three pages of search engine. You can read the whole article on how to make a website search engine friendly.