You are absolutely right Mark,
I use something similar on my page and I use MySQL. I even suggested it but if you dont use MySQL, then I agree that doing it just for this purpose would be unnecessary and can be easily done just by importing the text/csv files.
But you are absolutely right, that this is not only easier, but also offers other possibilities, I will think about what else could be done. On my page in the section I mentioned earlier in this thread, I do it slightly differently, rather than comparing current min/max and finding last date when it was warmer/cooler, I have a page that for example finds the last time it was -5 C, 0 C, 10 C, 15 C, etc etc. and same for rain - the last time it rained more than 5mm, 10 mm etc. Categories of course you can choose yourself. ANd it then also gives you the difference in time compared to today, so for example you get a table with the corresponding dates and times and next column something like "which was XY months, XY days, XY hours, XY minutes, XY seconds ago).
FUnctional demo:
http://meteopage.com/eng/console/console.phpon the right, click the icon for "Past weather"