I agree. I don't put them into Marketo. Instead, I upload them to SFDC. Then I send a report to our sales managers and ask the sales team to update the leads.
Although they aren't scored or pre-qualified, we tend to only do this for high level, obvious lead lists. For example, I tend to do this for international tradeshow lead lists. I don't do this for anything that doesn't seem like it would ever end up in the system (IE list purchases). Hope that helps!