If the UCD does makes a return, then it needs a revamp. A categorize function could be added, and with this implemented you can search within specific criteria, so if you're looking for a race car from a certain region or manufacturer, then you can categorize the UCD to do just that. And the same basically goes for any car type, region, manufacturer, and even whether it has aftermarket parts installed or not.
And speaking of aftermarket parts, I also believe tuned cars should show up within the UCD too. So if you're looking within the UCD listings, you might come across a car or two that has a few aftermarket parts installed on it, along with other non-tuned ones too of course.
In addition to this, I do think a test drive function to be created. I don't know about you guys, but I do sometimes buy a car only to realize that I just simply don't like it. If a test drive function was implemented, you'd be able to try it out and then decide whether you want to buy or not. The test drive function would be enabled for not only the UCD, but the OCD and the NCD too. Basically allowing you to try before you buy regardless of dealer type.