Integrate a separate script with Plugins?

Hello,

I am going to buy an events script and I would like to integrate it with WordPress (their front-ends).

Initially I was thinking to make several include files that will inject the functionality that I want in various places of the template.

Would there be any advantage of making my events script a wordpress plugin instead? Or plugins in this case would be useful only if I was planning to distribute them?

Also any other advice of integrating external scripts with WordPress greatly appreciated.

Thanks.