Yet another comparison (air-gap carb spacers)

Part of the fun is seeing how fast you can make the car go by tweaking/optimizing the little things about a combo rather than going out and changing cams, heads, carbs, etc.

Also, any time you change something, like a spacer, carb jetting may need to be changed to get the most out of it. And that's if your jetting was close to optimum to begin with! i.e.: If you install an open spacer and it goes faster, you may have been on the rich side without it.
It can be harder to figure things out at the track because most people don't have A/F meters. Drag strip times aren't a tell-all either because you have to be aware of many varying conditions that can affect the changes you made - temps, wind, shift points, etc. Your change may help. But if you, the weather or something else about the car isn't consistent, the comparison between runs may not be valid.

Like Mike said, "TEST, TEST, TEST". But you have to be aware of other influencing factors around you too.