That is a hard question to answer when if you had the best information, but its even harder without details. If they are models with rare tools, there is more chance value would go up, but if they are basic models they would go up in value more slowly. I think something many people forget is inflation. Almost everything will go up in value over time, but the real key is if it goes up in value more than inflation or if it goes up more than a basic interest rate. I'm always amazed when I watch Antiques Roadshow type programs and people are shocked by the price of their item. In most cases if it is worth a lot of money now, it was worth a lot of money when it was first made. If someone had taken the money then and put it in an interest bearing account, would that amount be more or less than a future selling price. The only time you should be amazed is if you bought it for a dollar and sold it for a much larger amount within a years time.