I haven't upgraded yet myself, but I'd say it's not worth paying $10 a month extra ($15 a month if you need txt) if you can't take advantage of 3G.
The (almost) only real advantage is the AGPS, you will have to ask yourself if $10/$15 a month extra is worth it or not...
I live in a 3G covered area, and still debating if it's worth the extra $$$ monthly...