I have tried #2 in the past. As @Keshav Trehan said a lot of folks (unless they have an urgent need - think doc consultation, order confirmation etc) will ignore their mail. (we had open rates of 32% - which meant 68% ignored the email). Click rate was 20 odd percent so which meant a very small funnel (corollary you get the most active demand capture because these folks have taken the effort to connect)
Also like you rightly pointed out, you will need to measure differently (definition changes)
I would not think of #2 as a different approach but as a subset of #1. So you get all emails and then you ask them to do #2 - for those that do you capture the most active demand and for the rest nurutre and push down the sales funnel