I was kind of in the same boat as you. I wanted at least the sport package, preferably M-sport and a nav. I ended up finding an amazing deal on a CPO with the sport package and no nav, so I ended up with that.
I had my car in the shop about a month ago and they gave me a 2012 328i loaner with a nav. After driving it around for a few days, I have to say I don't have any regrets about getting no nav. It was kind of cool, yes. It was cool seeing the album covers on the screen, yes. But to be honest, how often do I use a nav? Never, I have a TomTom that I use maybe once a year. So maybe if you travel a lot yea, you might be able to use one. But 95% of my driving is around the town I live in currently or the town that I'm from so I don't really need a nav at all. The iPod interface and other iDrive extras were cool but looking back they're not worth the extra money to me.
As far as how the iPod and iPhone works on a base stereo, it's surprisingly good. The best iPod navigation I've seen by far, that wasn't on nav system, was on the aftermarket Sony stereo I had in my old car, but the BMW stereo is surprisingly adequate. And I use the BT all the time to make calls, phone book shows up on the screen and everything. The only qualm I have is that it only gives you two lines and my old stereo had 5 lines of information. Other than that, I was pleasantly surprised at how well the iPod works on the BMW stereo.