If you collect die cast models, and they are all Formula One then decide the scale. Either 1:43, 1:20, 1:24, 1:64, 1:18, 1:6. The cost changes not due to size in many cases, more the rare find, the older version in mint condition. You need to keep your boxes, keep dust away as best you can, and more importantly, direct sunlight or powered lighting.
Fading takes place on decals and tyres, and the outer display cases and boxes. Keep in less direct light locations or away from power lamps that highlight the models.