First of all, Llorean, sorry about the double posting. I posted the first time, then realized that I had posted in the wrong folder. Won't happen again!
Now...
After following the suggestions posted here, I have completely reverted back to the original firmware, deleted ALL music that had been on there originally, and re-installed Rockbox with the latest build. With only the /.rockbox folder, the four sample pictures in the picture folder, and NO music files at all installed (accidentally deleted the two files that were on the player already -- the original firmware still displays them under artist, etc., but not in the browser), took a grand total of 45 seconds to fully boot to the main rockbox screen. It spent 23 seconds at the bootloader blue iRiver screen, and 22 seconds on the Rockbox title before giving me my menu selections. This just seems like an inordinately long amount of time to boot up.
I'm looking at my current settings in Rockbox itself, and this is what I see regarding settings for disk, etc.:
Disk Spindown: set at 5 seconds (default)
Directory Cache: No
My Version is: r13139-070412
Like I said, files copy onto the disk fine, as far as I can tell. A 225 MB folder took about 14 seconds to copy entirely. Single files copy on almost instantaneously. After copying the folder and single file to my disk, it still took about 36 seconds to load.
I guess it's just that I don't seem to recall having to wait that long for my player to boot before. If memory serves, I only had to wait about 5-10 seconds before. Maybe I'm just crazy. I don't know.