That depends if you feel that there are a lot of unnecessary elements and unnecessary custom CSS on your pages, then you better off to rebuild that pages from scratch. Try to build your pages using the native options of elements, don't use custom CSS or custom JS as possible.
Evaluate your plugins and think about it, which plugins do you really need and which is not. Deactivate and delete those plugins that you don't need.
I think rebuilding your website is not necessary, just remove those elements that you refer to as junk.
Hope this shed some lights,