Thank you for your replies. I waited about 1.5 days before posting here and it was still going along at 9.8 MB/s. FWIW, I have 7 ReadyNAS devices ranging from these to some Pro's and a pair of 12-bay's by another maker. So, I'm not entirely new to things...
FWIW, it's running 4.1.8 and has now been going over 48 hours. In my log, I have:
Mon Jul 30 17:39:56 PDT 2012 Volume C successfully added
The current time on the device is Aug 1, 20:55:04
It has picked up the pace and is saying it's 58% done. Checking here, at one point it said it was at 34 Mb/s, then 20, then 11... now 82... So, the rate it lists is variable (as is the ETA then) but it's been going now as I said for 48 hours and then some. (Oh, now down to 16 MB/s). At this rate, we're still talking ~3-4 days.
It's got 4 identical Seagate ST32000542AS drives in there. Yes, these are on the HW Compatibility list for the NV+. Health page shows "OK" on status for all but Disk 4, it being listed as "Resync".