Plants have won their war

So I was talking with my dad today, being home and all, and we started talking about health and how to eat right; and something monumental occurred to me. 

Plants have many ways of survival, including defensive measures (i.e. poison ivy), transportation (i.e. burrs, dandelion seeds), and methods of attraction such as beauty or some form of allure. Here I'll pause because something has occurred to me and I wondered if anyone else shares my idea.

In the tropics, survival is limited. Due to a much stronger diversity of species, wild storms and the like, most animals in the tropics reproduce quickly at need. Based on this theory, is it plausible that some plants evolve with attributes that make them more desirable to species?

We could talk about marijuana, that gives users a high, pleasant feeling and was incredibly valuable in durable clothing. Or we could discuss the Coca plant, where cocaine and cocoa arise, that gives users a feeling of energy and happiness. We could even discuss poppies, as they affect the users' mood. Hell, we could even talk about coffee and how caffeine has spread almost everywhere.

But the drug I want to focus on most, the drug that's been spread to every aspect of the market, the drug that could be responsible for the obesity epidemic of America, is Sugar.

When first introduced into Europe, sugar was treated as a drug. Doctors gave it out by the spoonful, literally. Today, sugar is in almost every food, and when eaten produces a "high" of satisfaction and energy. People talk about their "sweet tooth," that craving that hits and puts an image in your mind of something mouth-watering that you MUST have, and so you do. Where would we be without sugar? Pop, cookies, brownies, chocolate, white bread... the list goes on. And in all of those things, you consume something that leaves you wanting more.

Try eating a whole wheat slice of bread and compare it to eating a slice of white bread. You feel hungrier and wanting more sugar after the white bread, right?

So, in summary... plants have won their war. They figured out how they could be invaluable to a species and so made it to the top.

Your thoughts?