Realistically, if you are going to dabble with PHP, you will normally go towards a parsed system where you obtain all the data from tags, realtime uploads and forgo the default templates that come with Cumulus.
I agree with Steve in keeping the default templates as default usable as possible as there are many that simply are not ready for the leap to web design when they first start out.
Webtags, when uploaded can provide basically all the info the default templates provide with the exception of the graphs and you can still get those if you want.
These are very easy to implement and use.
http://wiki.sandaysoft.com/a/Webtags
My own version which stores the data differently and has self-display options to see what is in it.
http://cumulus.tnetweather.com/projects/tnetwebtags
Self-parsed:
http://cumulus.tnetweather.com/tnetwebt ... ?parse=sce