One reason to read old philosophy is that it is way more approachable. Most of the time, the approachability is an inverse function of the date the philosophical material appeared (understandable given our knowledge and thoughts have grown to be more complex throughout history). If you want to get into philosophy, reading a platonic dialogue (except Timaios and those with the Eleian) or one of the simpler texts of Aristotle (like Poetica) is way more easier than say reading Schophenauer, which is in turn easier than Wittgenstein, which in turn is probably easier than reading Derrida. Also, building up on examples of older pieces of philosophy, you have more tools for approaching the new stuff, because, surprise, it's built on not only the concepts, but examples and myths from and references to the old stuff.
And the best thing reading philosophy teaches to the non-academician is how to think with structure and method, avoiding dogma and bias, and embracing scepticism. Reading the dialogues has changed my life entirely because of that.
And the best thing reading philosophy teaches to the non-academician is how to think with structure and method, avoiding dogma and bias, and embracing scepticism. Reading the dialogues has changed my life entirely because of that.