This thread gave me some ideas, and indeed I track now the players ratings (back to the beginning of the season).

I use LibreOffice to make a few charts

- XY chart of past ratings on each played match, with moving average (green) and polynomial (red) 4-points trend lines
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- ratings frequency distribution, to see how often each rating value is obtained.
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I also have an adjusted rating XY charts, in which I give a penalty to ratings gotten against weaker teams, and a bonus to those against stronger teams, so as to smooth the opponent's strength differences.
In my mind, playing against a weaker team should always give you somewhat higher ratings (and the other way around).

I found this quite helpful to select my starting 11 and in the decision of replacing a player.

Many thanks to Khris for starting the discussion.