Jogging Stroller - Double, Single...or neither?

I'm debating on whether or not to get a jogging stroller. I don't need a new single stroller for Little Miss, she can use O's old one which I still LOVE!! (Chicco). I am debating a double stroller, or a sit and stand, so if we are out and about on a long day trip, O has a place to land if need be. Well if I'm going to spend the money to get a double or a sit & stand, I might as well get a double jogging stroller, so we can use it both for daily strolls, jogging/running, and long day trips where both kids may need somewhere to take a break. But....is it worth the money? Most double jogging strollers are anywhere between $200-$800. The one I am looking at (Baby Jogger City Mini) is $399.99 regular price....so is it worth $400.00?? I wouldn't use it as my everyday stroller. The main purpose of this stroller would be for walks/runs through the neighborhood and long day trips or any type of trip where we would be out and about w/both kids.

Troy is training for a marathon, and I am going to train for a 1/2 marathon once I get the release from my Dr....so we would be running/walking. I know the jogging strollers are a pain in the butt to push while run...but that would just make running alone easier right? I just don't see us both having the opportunity to run and train without some type of running gear for the kids.

O will be almost 4 when Little Miss arrives, so is he too old for a jogging stroller? Is it worth the money? I know in the beginning, if I'm walking around the block, I would need something for both of them. O still isn't riding a bike or anything so it's not like I can have him ride a bike next to me while I walk or run. I don't want to use the kids as an excuse not to exercise either.

So....should I take the risk and purchase the stroller, or do I just deal w/what I have?? Decisions Decisions!!