The L3000 is the only flagship headphone I owned that I felt was severely overrated. It's a beautiful headphone held in your hands, and it has that amazing scent from the leather, but the sound quality it puts out is nowhere close to the price they command on the used market, and I formed this opinion when they were selling in the $2500 range used. If they are really commanding close to $4k used now that leaves me just shaking me head in amazement and confusion. They can't even begin to touch the LCD2, so other than their being a limited edition I don't see how they continue to maintain their value.
The R10 I can not comment on having never heard them, but I have owned the CD3000. If the CD3000 sounds anything like the R10 then I would personally avoid them.
I'm a huge AT fan, having owned every wooden model and three different pairs of L3000s over the years. I wholeheartedly agree that the L3000 is overrated. For me, its coloration is extremely disagreeable, so much so in fact that I'd place it toward the bottom of legendary flagships personally. Interesting enough, it was one of my favorites when I was first starting out in summit-fi, and over the years it just grew more and more atrocious sonically to my ears. Though I also agree that it's a true piece of art, and holding it in one's hands is a joy unto itself. The use of leather on the cups is a brilliant and unique decision.
Regarding the R10, it is sonically a very different beast from the CD3000 overall, though their DNA is similar in certain respects. Sonically the R10 is a truly magnificent headphone and is definitely more deserving of its legendary status IMO, though it's still overhyped. The problem with the R10 is that it's simply too much of a gamble for all but the most serious collectors, as age hasn't been too kind to some sets and Sony no longer offers support or even spare parts (you'll find them on ebay from time to time, but at ridiculous prices).
I can wholly understand why the L3000 keeps its value. It's limited to 500 units worldwide and has garnered quite a reputation. Such is summit-fi. A lot of the market is "manufactured" by people less interested in headphones and more concerned with turning a profit, so they hype headphones to kingdom come, fostering this image of the "legends" of yesteryear. Since head-fi is a growing hobby, a lot of people are entering into the world of summit-fi for the first time, and they're confronted with a dazzling array of flagships that are no longer readily available, flagships that possess a certain allure and mystique that goes along with the past. In and of itself there's nothing wrong with that, unfortunately these individuals will often pay the ridiculous prices that flippers ask for, being told that the headphones are N.O.S. or otherwise like-new, that it's a more desirable "early model" or "late model" or "bass light" or "bass heavy" or whathaveyou. Basically one of a number of false justifications for their price which just happens to be more than other ads.
Coupled with the practice of people not retaining the prices on their old ads, and you get a situation where desire outweighs sense, and the truly unfortunate outcome is that it thus establishes a precedent: now the seller (or another seller) will point to that sale and demand a similarly high price for the next one. Flash forward to a year later, and you get "well that was the price a year ago, but now it's naturally higher!" Why is it naturally higher? People just take for granted that these prices are going to go up every year. When it comes to headphones with extremely low numbers, you also sometimes get individuals who buy up a whole bunch of them and literally drive the market up on their own. It happened (and is still happening on Ebay to this day) with the Sennheiser Orpheus, and some folks tried it with the L3000 a few years back.