I don't collect per say. I have display shelf and busy figuring out one for my premiums as I have around another dozen or so premiums that aren't on the display. So will be setting up a premium only display at some point. I don't buy many cars as I generally only buy cars I'm interested in and not for the value,, but I've gotten into customizing some cars for friends (like making 1:1's of their actual cars etc.).
Here is my office shelf (all mainlines with a mix of some cars from my youth - rs200 etc.)
One I recently did for a friend. Took 'n neonriders Focus RS and turned it into his ST: