Is AES/EBU digital cable/connection all that?

In my experience (knowing that others have had different experiences), in comparing exactly matching cables, for me the answer way Yes!.

This will probably system dependent. In my own system I have compared AES/EBU to BNC terminated SPDIF cable of the same brand and I prefer the balanced AES/EBU. I have also read others who prefer the SPDIF. I would suggest you try both, if you can borrow a cable to try out, and then decide.

Very dependent upon transport/DAC combination. I've had both terminations work best in different setups. In my experience AES/EBU cables have a little more air and/or warmth in mids and bass, this added air/warmth has been problematic in one setup as it caused a bit of bass boom.

See if you can borrow an AES/EBU cable to test it out. At the very least pick up the cable used so you can just flip it if you don't like the sound. If you don't try it you'll always be wondering, but it's certainly not gauranteed to be better than the RCA cables that you have now.