Wow, that wget command is tedious! Here's what I've got. Wget -q is quiet, -N overwrites the file if they've been changed and -i defines an input file.

% cat /etc/cron.weekly/sa-rules-update
#!/bin/sh
cd /etc/spamassassin && wget -q -N -i /etc/sa-rules-thirdparty

% head -3 /etc/sa-rules-thirdparty
http://www.rulesemporium.com/rules/71_sare_redirect_pre3.0.0.cf
http://www.rulesemporium.com/rules/70_sare_bayes_poison_nxm.cf
http://www.rulesemporium.com/rules/70_sare_html.cf

Cheers,

Guillaume