RNS315 is the obvious upgrade from there. You should get a DAB one for around £300. Has built in Bluetooth, so that's a bonus. Should do everything you are looking for.
Alternatively, RNS510. It's the top one, but doesn't have BT. You need a new one for DAB too, so around £400. For BT you can either go for a Fiscon or Parrot. OEM is too expensive usually.
Either way, you will likely need a new CAN Gateway. Usually around £50 coded, or you can pick them up for £30 or so on ebay and code yourself.
If you are happy enough with the nav system (easy enough to upgrade firmware, apply "crack" and burn latest maps), you could just add a Parrot system, letting you get your BT, USB, SD + Ipod.