Problems, and power are two different things.
All things being equal, a more powerful spark will create a higher cylinder pressure which in turn will make more power. Power of the spark is determined by the voltage, not the electrode material.
The amount of voltage required to jump accross the gap of a given type of plug is determined by the plug gap. A smaller gap requires less voltage, and a larger gap requires a greater voltage. There is a way to reduce the voltage required to jump the gap. Install plugs that have more edges that the spark can easily jump, or use a special electrode material, like platinum. (more efficient).
Before everyone runs right out and buys platinum plugs, know that "platinum plugs" produce a less powerfull spark than a standard plug at a given gap using the same voltage. This means that if your ignition system can provide enough voltage to jump the gap on the plug all of the time, every time, the platinum plug will provide less power than it will with a standard plug. The fix would be to widen the gap, and that requires votage that a stock system just does not have.
Will they work? Yes
Are they more subject to foul? Yes
Will they make less power? Yes
Are they really worth it for an older engine? You have to decide........