You are absolutely right, there a many variables to consider. Are you both skilled at or near journeyman level?
You're obviously beyond a start up, but still working out of the garage unless its huge and you have lots of capabilities will limit your revenue potential. Face it, some bigger companies just won't deal with home based businesses.
Not knowing what types of work you do the most of makes it impossible to arrive at a revenue stream you should be at. The figures another poster suggested seem really high for a home based business with two people working in a small to medium sized midwestern town. That is, unless you have lots of great equipment and are doing mostly higher end, high skill jobs and/or some electrical signs. You know your overhead and work load better than any of us, so only you can tell us what types of signs make up the majority of your days.
If you're doing mostly banners, dibond, coroplast, MDO, dimensional letters or HDU signs, etc.. I'd think a reasonable volume for two experienced and fully capable people in your type of scenario might be between $75k-$100k per person.
$2,500 per week for 50 weeks per year is a $125,000 gross.
How hard do you feel you have to work on a week when you do at least $2,500? Are you doing that much every week? Does a $5,000 week require some really long days? I'm just trying to gauge where you're at before I spout off some figure that you should be doing or consider yourself a failure.