.MOV for Long Term

Your analog conversions are a poor quality source to begin with and you will not get anything other than standard definition quality no matter what the container your use.

I am converting my family's old VHS home videos to digital using Roxio Video Capture. It works great but the one question I have is this...Is .mov format good for long term storage of the files? Should I convert to something more universally used such as MP4?

Both MOV and MP4 are essentially just file containers. However, on a Mac, use of the MP4 container normally limits codec use to MPEG-4 (chapter 2 or chapter 10) video and MPEG-4 (AAC) audio while the MOV file container is generic and may used to store any available compatible compression format—including MPEG-4. Since H.264/AAC is the normal default combination used on most current Mac systems, you should probably check the stats for your current MOV workflow. It is likely the stored data is already being compressed as MPEG-4 audio and video data in which case the data stored would be the same whether encapsulated in MOV or MP4 file containers. In fact, in most cases the extension can usually be changed from one to the other without affecting playback. If, on the other hand, your Roxio workflow allows you compress your old VHS tapes as Apple ProRes4-2-2 video with LPCM audio, then I would definitely use these compression formats for archival (long-term) storage since they maximize the potential for quality during later editing. (I.e., their only major disadvantage is an increased data bandwidth resulting in larger files.) If the Roxio hardware is compressing the analog data as DV content to the MOV file container, then you are probably better off keeping the DV files for archival use rather than switching to MPEG4/AAC MP4 files if you plan to do any future editing of the material.

However, as QTKirk already pointed out, overall quality will ultimately be limited by the quality of your source VHS content no matter what compression format is used to archive your data. If your question was meant to determine whether or not to reconvert files created directly by your Roxio Video Capture workflow, then you are probably better off not reconverting as this could potentially degrade the quality of any new files.