Your point is well-taken, and I'm sure experience will help me tremendously, but I see I may not have made myself clear, in that I was speaking not of just reaching level 10 in a skill, but in this case:
Master Inventor
At 100 big inventions built, you unlock this beauty of a reward. Big Inventions consume 20% less scrap, sell for 10% higher value and are completed about 10% faster. All widgets and toys are also built 'Masterfully' and jump up tremendously in value. This makes cheap toys fast money makers.
Those kinds of skill challenges are hugely time-consuming.
And way to go on that Wishmasters challenge!!