I wouldn't change the speaker wire for those speakers. For a more radical setup, I would consider it, but MB Quarts and other higher end speakers are installed all the time with the stock wires on the car.
I would add any sort of amp on them. I've seen a ton of stock radios, with stock speakers with an amp of them, and they sound much better over stock.
And the polarity on the speakers doesn't have to be "correct." You can actually switch it up and see if you like the sound that is produced with it flipped better.
If you are set on using the stock head unit, then definitely try a little amp. If not, you could get a head unit (I like Alpines), and power it off of that. But that still might not be enough for the upgraded speakers.