You won't have apps that utilize both cores so it won't really make much of a difference now. It's kinda like the 4G scene. What apps will you use that need that much bandwidth? Surfing the web? Use your computer if you're doing something that intensive.
Dual core phone? As in the LG Optimus 2X? Tegra 2? Good bye battery life since NVIDIA won't be all about battery consumption/preservation.
Until games and apps really utilize both cores and are optimized for it, it may be best to not worry about them. Need to have the latest and greatest and have the money for it? Then by all means. But if you're worried about being locked-in for two years, a one year contract may not be a bad idea.
I would say get what you like now, whether it has DC or 4G or not, and do a one-year contract. This time, next year, we'll see a bigger emphasis on both of those, or at least the DCs. Then devs will focus on it more and make it more practical to own one.
I'm still not sold on 4G, other than the speed, for my daily applications. Considering it's $10 more a month and is capped at..2 GB? It doesn't seem to be a value right now. Wit 4G, you will blow past 2 GB in a jiffy. Even 5 GB might be possible, for me at least, to bypass on 4G. Battery becomes an issue on this too.