I don;t ever recommend a 27 month old piece of technology, EVER! Yes, the 3Gs is a nice phone and is most likely better than what you have, but with cell phone contracts you have to keep it for 2 years. So in 2 years when that contract is up you will have a 4+ year old phone. At that point will it be able to do what you want it to do, can you get support for the product, will you be able to find a case that fits, etc?
IMHO, wait a few weeks for all of these iPhone 5 rumors to die down. If there is going to be a new phone, the 4 price will drop.