XRCD, as you seem to have deduced, is a mastering process. The resolution, and other technical details, aren't really important. The JVC guys simply do a very, very good job of mastering. That's why they sound better than the original releases (and they really do).
Yes, they start with good original recordings, because what's the point of carefully remastering a lousy recording? But the product demonstrates what good mastering can do.
As for SACDs, I happen to think the primary reason they sound better is also that they've been remastered, rather than because the extra resolution makes so much difference. Assuming I'm right about that, the XRCD/SACD choice comes down to who did the better mastering job. Given the track record at JVC, I'd bet on XRCD in most cases.
Yes, they start with good original recordings, because what's the point of carefully remastering a lousy recording? But the product demonstrates what good mastering can do.
As for SACDs, I happen to think the primary reason they sound better is also that they've been remastered, rather than because the extra resolution makes so much difference. Assuming I'm right about that, the XRCD/SACD choice comes down to who did the better mastering job. Given the track record at JVC, I'd bet on XRCD in most cases.