I purchased a nice bran new 2 piece set for the "Frunk" (or for behind the seats) in matching colors for my 09 R8. Osman was the supplier and a very patient man dealing with me as I hemmed and hawed over the cost for some time. He sold them at a very fair price given their availability or lack thereof. They are extremely nice pieces and very well made. Unique for sure and something I had to have. The luggage (IMHO) is one of those items that while expensive can add value to a car over other upgrades people consider. The two cases I have are different which was surprising. I thought they would be the same but one is a suit case as you would expect while the other is like an over-sized brief case with places for phones, lap-tops etc. Being a frequent attendee at high end car shows, you'll find fitted luggage in some of the worlds great marques which I feel adds to the panache of the car.
The fitted luggage is definitely one of those nice touches that adds to the panache, as you say - but I also think there's just a nice "romance" to it. These cars were designed to be used, and what better way than a road trip... seeing the sights, enjoying the drive. The fitted luggage, made from the same materials as your car, just helps make it feel that much more special. Is it completely unnecessary? Sure. Does it really help "immerse" you in the R8 experience? I think so. And I think that's why these fitted luggage concepts have been staples of high end cars for decades.
I think Audi actually did an outstanding job with it. Some manufacturers literally just contract a nice bag manufacturer to create some luggage and stamp a brand/logo on it. Audi actually went out of their way to make these pieces feel like they're an extension of the car. The fact that they're made of the same leather, stitching, carbon fiber, and alcantara, just immediately gives you the impression that it's part of the R8... before you even notice the embossed "R8" logo or "Audi Design" text.
Part of the reason why they're so rare, though, is because they were super expensive. The 5-piece set was $7,500 - for the black with white stitching. If you wanted to change the leather and stitching, the price went up. Aside from price, the other reason they're now extremely rare is that they were all made to order. They weren't simply made and stocked in large quantities. Each set was custom made, and delivery time was 4 - 6 months. See below listing from an Audi dealer that still has a now-defunct listing for it.
As Howie said, from time to time, you may see a set listed for sale. But they're becoming increasingly difficult to come across. I'm guessing very, very few sets were probably ever made, so if you're looking for one, I'd snatch up any set that comes along. You won't be disappointed.