Agree with most on here that the WRX is certainly better bang for the buck than the STI. However, the STI definitely does have some advantages: LSD, superior tranny (weak point of WRX IMO), etc.
I went with a base model and am very happy with it. As Vman mentioned, I'd only go Limited if you're importing from the US. I don't think the Canadian package is worth it. But to each his own.
Regarding NAV, I certainly would NOT purchase the OEM unit. Nav systems have to be the worst example of consumer gouging car companies have. I'm not suggesting you have to stick a Garmin on your windshield and have cords everywhere - get a nice new headunit (the stock subie ones are medicore at best) with integrated NAV and you'll be much better off.