I don't really COLLECT them. I kind of ACQUIRE them.
It would be supremely expensive to try and get one for every paint scheme for each year. I would suggest collecting cars w/ the 2 main sponsers or something really rare (like movie sponsered cars).
If you are looking for value only (and/or detail), get 1:24 scale. They cost a lot but gain a lot of value over the years. If you are concerned about space, go for the 1:64th scale. They are cheap (about $5 when they 1st come out), don't take up much room, and since they now mostly come in a blister pack, they are easy to hang and display. I prefer the 1:64ths for those reasons.
If I could afford to spend more money on die-cast, I would go for 1:24th scale, but you also have to buy something to display them in if you want to show them off.
Here is a scan of my only 1:24th. The box is 10 inches wide (front of car to back).
Here is a scan of one of my 1:64th cars. The whole package is about 6 inches wide and can hang on a pushpin stuck in the wall.
I hope this helps you with your decision.