After the 1900s, how much would an average RR employee have to pay for his new "middle range" railway spec pocket watch, IN TERMS OF HIS ONE-MONTH GROSS SALARY? (For example, watch price = 1.2 months salary.)

There's lots of historical wage info on the web if you care expend the effort to do a web search to sift through it.

I can give you one data point from my own family. My grandfather made $5/day on the Maine Central RR as a Master Mechanic circa 1920. I think this would have been toward the high end of the wage scale.

Wage and Price history in the US

If you use the above link as a guide and take the average overall wage of $438/yr in 1900 a typical $30 RR watch would be about 3.6 weeks pay, almost 1 months wages. If you get into the watches that were in the area of 50-100 dollars then you would be looking at several months of wages for the overall average worker.

Based on the average work for 1920 and using Edwards figures the $5x5=25 x 52 = $1300 and for that year the average overall was $1407 so the figures appear to be in the ballpark

In the 1950's, an Elgin 571, a Hamilton 992B or a Waltham 1623 were all priced at $72.50, if I remember correctly the prices I've seen in the old advertisments.

The average weekly wage in the 1950's, according to the chart Claude linked, was about $61.13/week or about 1.2 weeks wages to buy any one of the three RR grade watches listed above.

In the 1950's, one third the work would buy you a more technically advanced watch than in the 1900's.

Good thing or bad thing? Progress or regress? More apprecation for what you had or less?

Great response as usual, guys, thanks to all.

How does this sound as a 'rule of thumb':

In the 1900s, it was like buying a Rolex today,
In the 1950s, it was like buying an entry-level Tag Heuer today.