I'll second the idea to go aftermarket. I have the Nissan nav setup, and it's not great. I use google maps on my phone rather than the factory nav, if that's any indication of the ease of use. Buying a new CD every year is another issue (at $150 a pop) so again, google maps on my Android OS phone is the better choice.
If I were in your shoes, I'd consider a sub (see post above for a potential source (I've not used his services but reputation is good here on the forum)), an aftermarket head unit with better bluetooth integration (music streaming, not just phone), and an amp to really wake everything up. Some aftermarket speakers might be a nice add, too. The best part is, you can get this kind of system in pieces if you don't have all the coin at once. Maybe a sub and amp to start, then aftermarket head, then speakers, or something like that.