I don't have specific answers for your issue, but I have a general
observation: in many cases, it's easier to deal with argument quoting
issues (especially in constant arguments, as here) by making what Exim
runs just be a script that handles all of it itself.
Eg in this case, perhaps something like:
#!/bin/sh
exec date --date="$1" "+%A, %-d %B"
and then
${run {/path/to/script 2013-02-07} {$value} {$value}}
This is brute force but it gets you out of having to deal with all
sorts of quoting issues all over the place.
(This applies in general to 'have program A run program B with complex
arguments' problems.)
- cks