I am like you. I used to do 2 things with a 3rd type of fitness depending on the time of the year. 1 Was always present (heavy weights and Body Building) and I rotated between the other two which were aerobics dance classes and Kickboxing training. Now I can't stand dance or kickboxing and I am far from in love with BBing.
I am now in the camp that likes variety although I have my days and moments were I wish I could just pick 2-3 things and stick with it. I go back and forth. In fact I was just thinking about that today as I looked at my DVD collection- why can't I just pick a few instructors I like and stick to it? God knows I have about 1/3 of my collection still in wrappers and I know I'll never open most of them. I like my Leslie Workouts which I suppose is always a staple in my fitness diet. But with regards to everything else it's how the wind is blowing. I can like step aerobics for a couple of weeks, the Firm for a 2 weeks, heavy weights for 2 days, Band and resistance tubing work for a few months, and so forth.
What I have found is that I am actually in better physical health and shape these days vs when I stuck to the same 2-3 things all year, every year. Even though I wear a larger size now for one, and two, Leslie makes up a huge portion of my exercise, that little bit of variety each week or month has really helped me! Now I am a little different bc I do have a lot of old injuries I have to be careful of, but even then, I can go to bed most nights without pain meds and I took OTC pain meds 350 nights per year, if not more. I have been able to rehab my body, perhaps not to the extent that I would like and I still do have to baby certain joints, but I am pain free. I can walk 3-5 miles with no problems. Even when I did Kickboxing and grapling I didn't have the type of cardio endurance to walk for long distances bc I'd peter out.
I think really it depends on what your goals are. If you are looking for the physical look of your body to be a certain way, you will need to be more rigid and more structured with your activities. If you are going to health and wellness, regardless Fitness ability (Beginner vs extreme advanced) you have more slack when it comes to what you do and when or even "if". I like having my one staple just be I love it so very much. But I can no longer stick to rotations or a set schedule. I can't even commit to taking a class at the local gym 2x per MONTH because I no longer like being roped into what I am doing for fitness. I like the freedom and it's payed off for me and my goals. Like you have my days when I miss being the Gym Goddess and Kickboxer. But when I stop and think about doing that again, I cringe. I just cannot make myself sit still and stick to it, I feel like I'll bust out in hives or flames.
Variety is the spice of life for a reason. Unless you are running a marathon or training for a certain goal, physical goal, variety is very good. It helps the mind, body, and soul. It also helps to prevent overuse injuries and can help you to better balance the muscles and supportive tissues.