Are the rear brakes on a 04 ford focus only for the ebrake, or do they contribute to the stopping power?

The rears probably contribute approx. 25% plus or minus to the overall braking. Front brakes are about 75% of it. This is due to weight transfer when stopping,

True..but don't drive with bad drums or shoes regardless. If the rivets gouge the drums it going to get expensive..and that 25-30% is accurate, I agree, but you still need it. Not to mention if the shoe rivets push on drum, there will be a LOT of friction..enough even to ignite to fire.

Although it is now 10 years old, brakes are way to important to not keep in PERFECT condition! Yes, they absolutely contribute to the stopping power and it is imperative that you replace the shoes and drums if they are not perfect. What if you don't fix them? How about rear ending someone because you couldn't stop fast enough?? Even if no-one is hurt, you are responsible and liable! $100 bucks now is a cheap price to pay for safety.