Our culture's generalized path for how most of us begin and move through a sex life starts almost always with an intense turn on toward spontaneous sex. That if it's not spontaneous it's not hot or worth spending time doing.
When you're single, it's much easier to pull that off as we know. With children, extra demands on our time, more responsibilities, etc, the inspiration and time for spontaneous sex decreases naturally. Because couples are fixed on this sex form, as I call it, even less sex comes about. Thus, planning comes into it and the excitement of anticipation.
I tell my clients to take both of their options, in many cases, not just one. We know you can't plan on spontaneity rising forth, no pun intended. You can't wait for that. Do both. Plan hot sex dates -and- look forward to spontaneous moments.
I and my clients find that as their sexual sophistication grows, they will plan a sex night, put it on the calendar, get started with it, and during that sex session, spontaneous, hot, new things often happen; as well as returns to previous hot things done before that rise out of nowhere. That's another important way to enjoy spontaneity in sex.
Here's one way to create the turn on of anticipation: Your spouse sends you a hot email or text on what they can't wait to do to your body tonight, for example. That's attention! Fun, smoldering hot attention. Now you can't wait for it either.
Another point related to this is as you and your partner get better at giving each other sexual pleasure and big orgasms, your interest to have more sex, spontaneous or not, always increases.
It's simple. If the cuisine is amazing, physical and/or mental issues aside, you want more. You don't always have to be in the mood, the moment doesn't have to be perfect, none of that. I've started having sex countless times when I'm not "horny," but because of my skill set and often that of my partner's I know it's not going to be long at all before she and I are in a very different mood.
I understand the erotic of spontaneous sex as people know it. It's great stuff! However, there are other paths to great sex. Never bottle yourself in too much, especially with regards to this issue. I never would have gained the understanding of sexual pleasure making and had the amount of sex that I've had and have if I left it all up to spontaneity.
Real life things do get embroiled, but as I've witnessed in my own life and the lives of my sex life coaching clients, they deal with those things together much better when they have a strong sexual connection. Their sex life together becomes an oasis and an encouragement for standing by each other. That's that being in love thing. The trick is to stay in love beyond limerance. Reader, if you haven't heard of limerence, look it up. It's something everyone needs to know about.
Lastly, I know that psychology studies have placed the time frame for the end of the honeymoon phase at within a year. I've heard that the seven year itch is now the... three year itch, I think.
Science is an awesome tool. However, it has disadvantages. It is the proverbial microscope. It observes what's happening in our present. It is not as good at giving an accurate picture of the "what ifs...."
I wonder, what if many more relationships had the high quality sex life in place that I have with my partner. What if our culture experienced sex in a higher form than we currently know it? Would those stats be different? I'm running the experiment, if you will, every time I work with a client. My results thus far are a resounding, yes.