The type of external pump matters too- I had a LG4 (magnetically driven) that would calcify up pretty fast- 6 months was too long to wait to clean it. I replaced it with a shaft-drive Sequence, and have not had issues since. The sequence impellor runs cooler, so the calcium does not precipitate on it as much. I still need to pull it and clean it, but at least it is not wedging and failing at the 5 month mark.
As for heaters, cleaning them is a good idea, but would not affect efficiency. The heat has to go someplace, and passing though an inch of calcium on the way doesn't "use up" any of the heat.
As for the valves- I let mine gum up on me so much I had to replace them. I now use only dual-union ball valves, and love it. If they do ever seize on me, I can remove that individual valve and replace it with a spare, then go soak it overnight in vinegar. Thrice the price, but I’m thinking that it is worth it.
Zeph