does HDMI really produce a better picture & sound than AV cables?  if so, why? i have watched both ways & cannot really see any difference?

DVD's do not do 1080 but the player might.

1080i just means that for the i or interlace, they paint half the screen, then the other half... if the TV is analog. Digital sets undo the interlacing and show 30 full pictures per second.  1080i @ 60 fps is identical in output to 1080p @ 30.

Digital does do a better job than analog but for normal people, they'd have trouble telling the difference if the signal is clean.  A little bit of training will let you spot it but don't bother if you are happy with what you have.

RCA Cabling is analog, not digital. Quality lower but you won't see difference without training.  Upscaling will happen somewhere when the source material (those DVD's for example) is lower resolution than your TV.  You just need to choose if you want to bother changing it.  If the TV is 1920p, for example, to show any content that is not at that resolution, it MUST be upscaled.  This can happen at the player, the TV, or any equipment in the middle.  You can pick which is better at doing that.  Since you can't see the difference between analog and digital, don't bother with that setting.Current image level is called (incorrectly) 4K.  It is UHD or Ultra High Definition.  Resolution is 3840 by 1920 pixels.  The BIGGIE, more important than the resolution, is the color gamut.  Your DVD uses 8 bits per color or 256 shades of red, green, and blue.  UHD can do 10 or 12 bits depending on the set.  That is 1024 shades or 4096 shades.  The human eye can pick out about 4000 shades of red in studies.  This is by far, more important than the resolution.

As for when, years ago. (not gonna look it up)

So, if you need a new TV, look for UHD and check black levels.  Current sets, including yours, try to block 100% of the light for black and they can't do that.  But, you can use that to pick ones with good pictures for low money.

I would say they are in par with component hookup, though they are in a simple single wire format, however today the speeds of them are faster as the generations went by and yes today you could say they are superior than the last generation of hdmi and as of today blow component out of the water with their improved technology

There are too many questions in one here, 

but they are all valid.    

It would be best to consult in person with someone who can not only explain it all 

but also point out specific details in actual images on the screen.   

This is a matter for the TVs section.

Without knowing the makes and models of the TV and player in question, this is too stupid to answer.

Even if the changes in video quality are quantifiable and measurable, some of us are more audio people than we are video people.

But even then, we don't have room for 1,000 speakers.

https://www.tomsguide.com/us/4k-tv-explained,news-...