Is there a Solaris utility which reports the minimum free space on a file system over the preceding 168 hours (one week)? The concern with using a nightly df is that there might be intraday jobs which nearly exhaust disk space when they run, but clean up after themselves so there's no apparent problem when df runs.
I don't believe there is any built-in system that does this, but nearly every monitoring system I've ever used is capable of trending disk space over time (at whatever granularity your polling cycle is, over varying & configurable lengths of time).
If you do not have a monitoring system in place I would suggest checking out Cacti (if you just need trending) or InterMapper if you need alerting + trending. Something could probably be worked out using Nagios or any number of other solutions as well...
Short answer: no.
You could define a smaller interval between df runs as to catch this relatively fast running scripts. How fast a script will be able to fill up your filesystems depend on their size but it should give you an approximation for the worst case based on your disk speed.