A lot of the spamming at the SC2 tournament level is about staying warmed up so that when you get into a micro-intensive battle later on where all of those actions might count (splitting your marines to protect from AoE while target-firing the suicide bombing banelings, for example) you can do it. Doesn't make it look less ridiculous, especially in the first couple of minutes before the commentary has anything to really talk about so they try to act like stealing 5 minerals at that stage could somehow decide the game. But there is a slightly more reasonable logic to it than just speed running an RSI to look cool.

The original StarCraft also offers a lot of opportunities to use your "extra" APM to optimize around the godawful AI pathing and other "quirks" of the engine. It's not as bad as, say, DotA in terms of "this was a limitation of the original engine that is now a major cornerstone of playing the game well and if you complain about it you're just bad" but it's definitely up there. As the game goes on you'll usually see players start getting slightly more fast and loose with, say, optimizing the mining at their new base because at that point in the game splitting your focus that much is more detrimental even if you can move that fast.

I definitely ended up in the occasional spectator and campaign player for all that, though. Especially now that I'm starting to have creaky old man wrists of my own.