According to Kingwa the sound signature is the same and there is only a SLIGHT
improvement in terms of SQ. I wouldn't bother about upgrading or worrying at all about your RE1 being an old piece of gear. Upgrade only if you absolutely need the AES input.
If Kingwa keeps the rate he's putting gear out we might see the RE8 come out next year.
I however am wondering why Kingwa decided to wire only the AES input with silver wire and not the others.
I'm considering purchasing a pure silver BNC digital cable and it would have been nice to keep the digital part of the DAC with silver wire and the analog part with copper.
Another improvement is that he corrected the lettering in the back from XRL with the RE1 to XLR with the RE7.