The number does not mean anything specific. It's simply "the higher the worse". 23 is pretty darn high so I'd strongly suggest you run a realloc on that volume. I've seen customers with a value of 13 or so, who, after doing a realloc, observed a 2x speedup in their DB access times.
The threshold is always 4, this is the point where the filer suggests duing a reallocate. i.e.1 to 3 is good, 4 to (unlimited) is bad
Hotspots tells you if you have hotspot disks or not (i.e. your data is not distributed equally across all data disks in the raid groups or not). 0 is okay in that regard (everything >4 is, again, a reason to start doing reallocs)
I wouldn't worry about the time it takes or the CPU, both is not really a problem (realloc runs in the background so other processes always get priority).
-Michael