I'm new to the backpacking scene but quickly falling in love with the sport.

After borrowing some sweet Black Diamond carbon poles for a hike last summer I'm sold on the benefits of using trekking poles for any distance hike. Since then I have landed some cheapo Coleman from WalMart poles for free. Used them this weekend for an overnight backpack, hiking 20 miles each day for 2 days. Other than the grips being hard plastic and their being heavier than the ones I borrowed last year I can't say they particularly sucked goat eggs....but my question:

What is the benefit of purchasing a higher end pole over a lower end one?

In particular, what are the pros of spending more for certain features?

Are more expensive poles going to be more durable in addition to more lightweight?

What features should I look for if most of my hikes are going to be over a widely varied terrain, going from rooty to smooth to muddy to rocky?

Thanks!