No "ifs", "buts" or "maybes", this is the way to go. I did just this on my Panasonic frankenbike and was startled by how much weight I took off.

There may be some high-end light-weight cottered cranks that were manufactured back in the day but the odds of the OP having one of these are slim to none. Tossing this crankset in favor of an aluminum one will give you the best bang for the buck when it comes to reducing weight.

Do this and it will feel like you've gotten a new bike.