Re: You can't measure knowledge work
Depends which company you work for. Where I work, showing initiative like this would of course result in some additional tasks heading your way because you've optimised an earlier task and have free time on your hands. You deserve plaudits for that of course, but if you'd prefer to sit around doing nothing, are you really a model employee? Personally, I prefer to be kept reasonably busy - not overworked of course, but lack of stimulation leads to boredom and I don't find that good for me.
As for management, where I work management power is (amongst other things) measured as maximising productivity whilst minimising costs. If you can do the same thing as another manager with fewer people, and whilst maintaining a happy and motivated team working for you, that shows you are a good manager who is getting the most out of your team. Alternatively, if you can do a lot more with your personnel than another manager, get involved with additional activities that mean your customer is delighted with your team's performance for example, this also singles you out as a good manager.
Furthermore, employees showing initiative like this to improve efficiency of tasks are rewarded in a number of various ways (higher annual pay-rises, bonus awards with extra cash and other such goodies, etc).
Any company that determines manager power by headcount and not by performance isn't a company I'd want anything to do with personally.
FWIW (as a footnote), I've sat on both sides of the fence in my current company. I was an engineer for many years, I'm now a lower level manager. I trust my team, I let them get on with the work they specialise in without me poking my nose in and I encourage them to show initiative and innovation and reward this accordingly. I also shield the team from heat on those rare occasions when things do go wrong, because back when I was an engineer, that is what I considered to be good management.