I have a large number of pages having similar but not identical content. Example: site.com/dream_dictionary_flying and site.com/dream_interpretation_flying.

The problem is that although not being identical, they are sometimes on the edge of being duplicate content. The solution via redirect 301 in htaccess is simple and can be done in a minute, BUT, changing all existing links on the whole site from "/something" to "/something_else" would take ages, it would be thousands of manual changes taking x hundreds of hours.

My question is this; is it bad for SEO to have internal links that are redirected, or rather HOW bad is it? For the human user it would not matter at all but from what I have experienced, the search engines don't like it. Is there any rule of thumb here? Please come back with your thoughts and experience on this.

Thanks!