Should I use cache on data pulled from within files?
The reason the documentation says to not use it on static text, is because the cached data will be saved to the database, resulting in at least one database query (two if it needs to update the data). Database operations are fairly expensive compared to reading data from files, or running twig code, so in many cases this will be slower than just showing the text.

There's no way to know for sure if using cache tags will be a benefit in your case. It really depends on what exactly you're doing in your template, and where the bottlenecks in your system is. The only way to know, is to test it. If you turn devMode on, reload your page with and without the cache tag enabled, you could compare the response time shown in the console output under "Profiling Summary Report". This is the time it takes for the page to be generated by craft, which is what you'd seek to minimize using the cache tag. Remember to reload the page several times for each case and do an average, since the result will vary somewhat depending on what else is going on in your system.