I typically don't try to fix somethin' that ain't broke. JMO
I've heard too many examples of a download screwin' somthin' up that wasn't broke in the first place.
With a 2006 radio it may fix issues you have regarding the radio coming on when you had it switched off from a previous ride etc. There were a couple of other upgrades in the 8.19 version over what you have but I can't remember off of the top of my head what they were.
Where on the HD site do you find the software download? I have been all over the site using the site map and can not find downloads other than wallpaper, ringtones, etc.