Ok so I'm not 40 (30) but I can say that when I do less cardio, including less intense cardio and more strength, I have better results.
I have found the key is that I do better with total body workouts and use the occassional split for work on muscle imbalances. Although before this pregnancy, I just added on a few exercises throughout the week to accomplish the same thing. The second factor to this is like a couple of others have mentioned, I work in functional fitness. It's a multi-plane and multi-joint form of strength and it helps to shock the body but still stick to total body routines.
For cardio, I'm a walker. I've done everything from step to kickboxing (even trained in a gym with a coach) to sprints and cardio DVDs. There have never been anything that has worked better for me than combining walking with strength and that's held true since my teens. I've tried many things but why fix it if it ain't broke?!
Find a type of cardio or a few that you enjoy and mix it up. Cardio is great for heart health but the true key is to just keep moving throughout the day. I had a conversation with my mom this week and she's now 50 about this same thing. She said that in her 30s she could go and go but has come to realize that she gets plenty of movement (cardio) throughout the week by keeping busy around the house ie: cleaning, home repairs, building, dog walking, gardening, yard work, etc. We both agreed that over the years we've seen many o people that spend 1-2 hours at the gym or just working out most/every day and come home spent. They have no energy to chase the kids, scrub the floors, go for a long walk after dinner, and keep up with life without feeling exhausted and over worked. It's not the "exercise" name but what we do with our time that counts.
Build some muscle and stay active. That's what will matter and with time you'll see it improve your shape inside-out. Hell, I'm 30 and I have started living this way within the past couple of years and adore it. It's like the weight just melts off without trying (pre pregnancy but even keeping to a healthy gain during). If it isn't fun, don't do it and focus on strength first.