Actually you already own two phones with 1ghz processors so it will be insane choice to go for some single core phones like htc se or bla bla
go for dual core
after honeycomb which was totally for tablets now icecream is on the way and i think it will support and enhance dual cores
so 2012 is comming be on the safe side
my purchase is due after eid
surely going for dual otherwise iphone 4