I have a black RST, which I use for commuting and weekends. I upgraded the brakes to XTR and they are very very good, noticably better than the Deore brakes that were on my previous bike, whether it's worth the money tough to decide, but given that my bike was in memory of my in-laws money was not a ocnsideration. One other advantage of the XTR brakes, is that they're cartridge based so changing brake blocks is simple.
I must confess I bought every upgrade I could think of, so I probably went a bit over the top.
The only consideration to panniers I made is I got the lightweight Thorn ones. I don't intend to use the bike for expeditions so those are suitable and lighter.
One thing I wished I'd considerred was the dynamo. I now have a Arc HID, but wish I'd at least thought about a dynamo when I bought the bike as the HID interferes with my computer.