Of course, as you say, it could work the other way, and working could become more valuable because one worker could generate more returns. But that requires there to be more demand for everything.
Like, say, people eat only potatoes, and all work 8 hours per day to harvest just enough potatoes for everyone. If a machine could do their work, and they couldn't think of anything else to do, there would still be the same amount of potatoes, but less work to do.
Could your pay go down in the example? Theoretically yes, in practice we see the opposite. Economic development couldn't happen if it did. Although I suppose short term dislocations could lead to lower pay in the short term, before increasing long term?
Don't forget 'progress' is people increasing productivity. In a world where everyone has to work full time digging potatoes, that's all anyone has. If it only takes 1 member of the group to dig potatoes, that frees the other members to discover science, religion, chips. We are in a situation now where a fraction of the population work in food production, but we all have jobs and more wealth than potato growing us could possibly imagine.
That added productivity doesn't disappear, in our earlier example the owner of the means of production has captured all the value that I didn't get from it. He has to do something with it. Even if he puts it in the bank, that's possible seed money for a venture that ends up employing my 9 ex workmates.
Also don't forget that the one potato digger won't want to dig potatoes all day whilst everyone else sits around. If there's no reason to dig more he'll dig enough for himself and take the rest of the day off. Now you could entice him to dig for you in exchange for beans, because you know he doesn't like picking beans, and as you don't like digging potatoes. And of course I could offer to trade apples...
I think you may have this backwards.
If I generate $1 of value/hr that's kind of the maximum you can justify my wages being. If you give me a machine that increases my productivity 10 fold and the machine costs $2/hr then my maximum wage tops out at $8.
Now in this situation less labour is required, but the labour isn't less valuable. Obviously now you need a new industry to come along to employ the other 9 people who aren't now needed, possibly now servicing me and my newfound wealth, or possibly building the machines that put them out of a job.
'value' is what someone is willing to pay. My employer would have been willing to pay me a maximum of $1 and $8 pre and post machine introduction, so you could say my value increased. But I'm not likely to see much of that in the short term, because all my mates are now unemployed, and would be willing to do the job for their old pay, so my leverage is very low, so worst case I keep the same pay, in which the value of the job to me hasn't changed.