An important part of engineering is measurement. If we make a modification, we expect that there is a benefit. We could measure before and after with gas mileage and quarter mile times. If there is no improvement, then we have gained nothing with the modification. If there is an improvement, we have succeeded. If we don't know, then we have just been guessing. The important thing is that you measure something that is important to you and establish a baseline. Any changes you make should improve the thing that is important to you. If it doesn't, you need to figure out why it didn't work and try something else.
If we take the manifold heat idea as an example, we could hope for better fuel economy and better acceleration as benefits of adding heat to an engine that has none. In my case, I started off originally with a cold intake manifold in my 65 Barracuda when I ran a BBS 1bbl carb with headers and, once the engine was warm, the car ran great. When I installed the AFB afterwards, I always seemed to have an off-idle bog than only seemed to go away when I dramatically richened the power mixture and the bog disappeared completely when I installed my intake manifold heater. Because I knew that a small engine should not need so rich a power jetting, I reasoned that the gasoline was not ending up at the cylinders when it should. As I researched this further, it became obvious that I needed more manifold heat. I learned that smaller carbs make the engine less sensitive to intake manifold heat. Airflow through a small carb with a high pressure drop helps keep the atomized fuel suspended in the airflow.
You might think that my experience depends upon the fact that I live in a northern climate and this idea wouldn't be applicable to more southern regions where the climate is much hotter. However, the basis for my experience is with summer driving and it can get quite hot here in Ontario during the summer (often 30°C/86°F or higher). This would probably be cool weather for people living in southern American states though. Anyway, I found that after adding heat to my intake manifold in the middle of summer, my car completely lost its off-idle bog.