I've definitely decided to forgo iOS 6 at this time. I'll reevaluate my decision in the near future. Two of the major features being touted are pointless for the iPt4. Without GPS, maps are worthless; and Siri is nonexistent.
As to the iPt5, I'm definitely not upgrading. RAM is only 512MB, it lacks GPS, and the entry level model is priced too high ($299).