Is it necessary to keep iMovie libraries

I have been using iMovie to digitally preserve familymovies (8mm tape & film) that might otherwise become outdated media in the future. As a result of this my 1TB external drive has filled up with exported iMovie libraries and MP4 files created from the libraries, not to mention the raw MP4 or MOV movie files.

Here's my question. Now that the iMovie projects have been created with titles and transitions to my satisfaction and the projects shared to MP4 files is it necessary to keep the iMovie libraries? Should I at least move them from the external drive to DVD-RW media for possible future use? Ideally I would like to have a 4TB external drive to store all libraries, MP4 files and raw files, but right now that doesn't fit into the budget.

My goal is to use the MP4 files and burn them to DVD using some 3rd party software since iDVD is no longer useable with Yosemite.

Any suggestions?