Not sure about the best way to go about this (if there is one). Here's what I have and what I'd like to do if possible:

During the 1990s, I recorded a number of videos using a camcorder, a few directly onto VHS tape and the others onto Mini DV tapes.

In the early 2000s, a friend of mine got a Memorex box that, when connected between a videocassette player and a computer, could convert on-tape videos to digital files. I borrowed it and then used a video editor (whose name I can't recall other than that it was made by Turtle Beach) to burn the resulting files to Memorex DVD+R RW discs.

MediaInfo sees the following folders on those DVDs:

AUDIO_TS (which is empty)

VIDEO_TS (which contains 8 files):

Video_TS.BUP 6 kb
Video_TS.IFO 6 kb
VTS_01_0.BUP 42 kb
VTS_01_0.IFO 42 kb
VTS_01_1.VOB 1,048,160 KB (in the example that I'm using here)
VTS_01_2.VOB 1,048,510 KB
VTS_01_3.VOB 1,048,016 KB
VTS_01_4.VOB 763,552 KB

Looking at the VTS_01.1.VOB file with MediaInfo, I see that the format is MPEG-PS and,

Video:
Format: MPEG video
Format version: 2
Format profile: Main@Main
Bit rate mode: Variable
Bit rate: 7871 kbps
Frame rate: 29.970 fps
Scan type: interlaced
Compression mode: Lossy
Audio:
Format: PCM
Format settings: Big/Signed
Muxing mode: DVD-Video
Bit rate mode: Constant
Bit rate: 1536 kps
Sampling rate: 48.0 kHz
Bit depth: 16 bits

Two years ago I wanted to have a backup of those DVDs on one of my external drives, so I used Wondershare Uniconverter to convert the DVD videos to .mp4 files for backup The same video that I show above is now also this .mp4 file:

General:
Format: MPEG-4
Codec ID: mp42
Overall bit rate: 10.1 mb/s
Video:
Format: AVC
Bit rate: 9 999 kb/s
Frame rate: 30.000 fps
Color space: YUV
Scan type: progressive
Audio:
Format AAC LC
Codec ID: mp4a-40-2
Bit rate: 128 kb/s
Sampling rate: 44.1 khz
Frame rate: 43.066 fps
Compression mode: Lossy

Here's the issue:

Because most of these videos were shot outdoors, they all have anywhere from a moderate to significant amount of background noise (traffic noise, leaf blowers, lawn mowers, etc) which is distracting. I see that PowerDirector20 / AudioDirector has some options for fixing audio, including Speech Enhancement and Background Noise Removal. So I'm wondering if the audio on these old videos can be cleaned up in that way.

So here's my question: Because I have all of these videos in two formats (on DVDs and also as .MP4 files), which 'source' would be better to bring into PowerDirector... and how best to do that? I have read that it's always best to work with the original video files because any kind of conversion process inevitably results in quality degradation, but in this case true originals (the tapes) are long gone.

As far as the video quality, the DVDs that came from the mini-DV tapes look pretty decent (though could benefit from some color correction occasionally) when viewed on a tv; the DVDs won't play on my computer. The oldest video, which was shot directly onto a standard VHS tape in 1992, would need the most work on the video but less on the audio.

The .MP4 files made from those DVDs look the same as the DVD if I plug the drive into my player's USB port (my tv's USB port won't recognize either of my external drives) but those same MP4s look horrible if I play them on the computer. The audio quality is the same regardless of what is played where.

What would be the best approach to trying to clean up the audio (which is narration with distracting background noises) on these videos, and what file format would be best for that?

I do realize that every time a video is encoded, it gets somewhat more "trashed". I also see that PowerDirector supports importing .VOB files - would that be the best way to approach this? and if so...how? Or I could do a fresh DVD-to-MP4 conversion using Power2Go 13, if that would make the workflow simpler.