Any way to get more space for editing post excerpts

Depending on the context, in which you would like to make these changes, I’d simply remove the metabox from that certain post type. Then add another metabox above the editor for your excerpt box.

The downside: you can not use get_the_excerpt, the_excerpt etc. anymore because that metabox doesn’t exist any more.

Have a look at this post

How can I put a custom meta box above the editor but below the title section on the edit post page?