Hopefully my post adds to the conversation, I've gone a slightly different direction.
i.e. not focused on collecting per se, but more on the reasons why the two hobbies are different, and therefore inherently have some different factors related to collecting... full disclosure: I collect both categories.... The words below were written by Pat Dennis. He is a friend of mine. He designed one of the most popular HO slotcar brands from the 1970's called TycoPro. He has some interesting insights that he's posted on a slotcar forum, I've paraphrased some of it to make it comprehensible as part of this thread: http://www.planetofspeed.net/phpBB3/viewtopic.php?f=6&t=6410&start=60 His post was meant to describe the similarities and differences between real cars and HO cars. Pat has a life time of experience in both worlds. Alot of his comments hold true for a comparison between slot cars generally and R/C cars.. Here is what he says: .... the similarity between a real racecar and a slot car stop after the fact that both have four wheels and a propulsion device. An analysis of both follows: Real Racecar * An actual racecar has a functioning steering system and a decision-making on-board driver. * Is operated within the limits of adhesion in the horizontal plane through the experience (through intensive practice) and the "seat-of-the -pants" feedback. Exhaustive studies have proven that a driver who can maintain the smoothest transition of acceleration, braking and sideload G's turns consistently faster lap times. * These limits of adhesion are derived through engineering of the car - suspension control, braking design and materials, and tire technology. Additionally, aerodynamics which impart down force enters into this. * Actual race courses are typically glass-smooth, with somewhat gradual elevation changes Slot cars * A slot car follows the dictates of the slot and a remote operator that only controls the power, and is totally dependent on maintaining the guide pin/blade penetration into the slot. * There is a peculiar force, unique to slot racing that occurs when a slot car is subjected to a curved section following a straight. The front end of the car is violently jerked to one side upon entering the curve - remember that there is no lead-in to the radius, no ability for the driver to "set" the car's suspension upon entering the curve. This is what I referred to as a "spike force" acting on the guide pin/shoe. In a conventional race car this would be roughly equivalent to have the car struck on the front corner by another car at a great rate of speed at nearly right angle to the direction of travel. In an attempt to reduce the effects of this "spike", the TycoPro used a guide flag with a slight lead-in to attempt to "set" he car before that force arrived at full force. (note that the guide flag has the blade extending ahead of the pivot shaft). * Additionally, the upward force of the pickup material (spring-loaded rigid "skis or flexible contacts, braid, etc.) needed to insure electrical contact adds to the upward force of the front, lifting the guide device. * There is an additional force consideration, and that is the action/reaction of the pinion gear attempting to "climb" the crown - lifting the front of the chassis on acceleration and under power. This force is reversed upon deceleration - effectively forcing the guide flag/pin downward. This is the reason that an HO car responds so well to a short "off" to the controller approaching the curve. This is as close to "setting" the car for the curve as is possible for a slot car Note that this forward weight transfer exists in a real racecar, but is much less critical.
.......................... So in the above comments, you can readily substitute the word "R/C car" for "Real Racecar".... and even though they seem to appeal to the same crowd (to a large extent they obviously do re Automotive etc) but for a significant part of the corwd in each would be passionate about arguing the merits of one or the other--which sort of pushes "value", and hence collectibility
One other interesting thing, is considering where the slot car hobby and RC hobby merge: miniaturization is one part of the obvious common ground...