Just updated Jenkins and all plugins as of 2015-03-31 evening EST

Consider mentioning which versions you used before, and which you installed now (Jenkins has two release lines, so the date isn't sufficient, aside from the fact that you don't provide a list of plugins.)

Where is the text for the failing job configured? (Job Name, Display Name or Wall display Name)?

Consider mentioning which versions you used before

You may have missed "Don't recall previous versions" which suggests I did consider mentioning versions.

The current version of Jenkins is 1.596.2. On the configuration screen there is a "downgrade to 1.596.1" link, but I can't be sure that was the previous version that was installed or if that's just one version back.

The current version of "Wall Display Master Project" is 0.6.30. There is a downgrade link to 0.6.28 but again I can't be sure that's just one version back or the version that was working before.

Rolling back both of these does seem to restore parameter substitution.

Where is the text for the failing job configured?

It's configured on the job's "Walldisplay text".

I can't be sure that was the previous version that was installed

but again I can't be sure that's just one version back

It is. Jenkins offers to downgrade to the previously installed version (unless you mess with the plugins directory and install by copying files around).