Usually it's the cars that were hugely popular (AE RC10, Tamiya Sand Scorcher) that end up being valuable. They are definitely not the rarest cars, but demand is usually much bigger than supply, making them easy to sell, too... That is, before the time or re-releases.
In some cases, cars were popular but remained elusive dor many due to its price at the time (Tamiya Avante, Kyosho Optima, Tamiya Mountaineer/Bruiser/etc). The price keeps sales lower, so these cars often become valuable too...
And then there is the rest. Some cars there actually may be very few of; others there are no nice or new examples of anymore. So you may find someone willing to pay good money for a nice example. However usually it means your car will be for sale for a very long time. Sellers tend to lower their prices in an attempt to get it sold anyway. As a result, these cars never become valuable.
For the D4, I don't think it had the popularity to become a valuable car. One can also wonder with the market nowadays if any model will ever become as valuable and iconic as those we had in the 80s and 90s. As for the D2, I think it was never released; instead HB went back to the drawing board in 2010 or 2011 for a mid-motor buggy, which ultimately became the D216... No resemblence there anymore. So to a hardcore RC enthusiast, it might be valuable if you have one, if it is complete and has no broken parts.
If you like rebuilding cars, I'd just do it for fun and see where a sale would go from there
