I was missing the possibility to pass a parameter to a crontab line, so that I can do different things on different days.

e.g.
We have a linux that is built every day except Saturdays (~1h) and on Sundays we run a clean build (~10h), where Saturday is reserved for other projects that run a clean build.
The only way for me was to create a conditional build step. It blows up the job configuration and gets decoupled from the crontab:
So when someone changes the crontab from Sunday to Saturday for clean builds, he will also have to change the day in the conditional build step.

My proposal is to extend the crontab syntax by something like:

MIN HOUR DOM MONTH DOW % PARAM1=VALUE1,PARAM2=VALUE2

This would than schedule a build with the given parameters.

Would others be interested too?