I haven't had a500 with hd ealier, so I 've forget how ugly and limited it is. Is there any programs to enchange it ?
Try and pick up a fredfish CD (the one that came with the CDTV would be great) and have a look through that.
There are lots of silly things to make 1.3 look better including things like copper bars as the background (those are the HAM 4096 colour bars like found on uridium2 and other games) you can add the tracking eye's and all that stuff too.
Dont know of any icon enhancements for 1.3 though, although you can make some real nice icons with the four colours if you wanted, I remember putting a disk in once and this massive disk icon came up, it was about 500% larger than the normal one.

But anyway PD is your friend