I was in the exact same situation as you a few years ago. I chose to buy a smartphone, but it weren't really that fast (HTC Magic) although the customization on Android is much better than iOS. I kept using my iPod Touch as my music player (and used few apps not available on Android) and used my smartphone for pretty much everything else. That was until I upgraded to a Galaxy S. I bought the phone used and sold my Magic and iPod Touch for 135 $ combined. My Galaxy S cost me 305 $, so it wasn't really that expensive.
A 30 $ data plan? That sounds very expensive. My data plan only cost me 12 $ per month and SMS, MMS and 1GB data is included in the price. Data plans might just be more expensive in the US, I don't know.
I love the GPS in my smartphone! Whenever I'm lost my, phone is there to help me, and it is so convenient if you go somewhere you have never been. That is one of the biggest advantages of a smartphone in my opinion.
Just make sure you buy a powerful phone if you choose to switch to an Android. It doesn't have to be the newest phone (maybe Galaxy S II or something like that?).