I will agree on the constant parking lot "look backs" as being a good sign. I realize that the X5 M is fairly derided amongst M purists (and I get it), but at the moment my fiancé and I only have space one for car each, and only an SUV fits our needs, so that's what I have. That being said, I truly think the F85 is simply one of the best looking SUVs ever built, period. I love the more classic BMW design in the front, and the whole thing is very understated. The average non-car person doesn't give it second glance, but other BMW owners have given me plenty of compliments on it in parking lots, getting gas, etc.
Another sign is getting to drive a car that is ostensibly nicer, but still wanting to be back in your car. While the X5 was in the shop, I was given an M850i loaner. I drove it for nearly a week, and while the handling was impressive and the new N63 is excellent, it just wasn't the same. I got back in my car and it felt like seeing an old friend again.
I usually do not keep a car more than a couple of years. The longest I ever kept a car was my '06 Altima SE-R 6-speed, which I had for over 5 years and I put over 70k+ miles on it. I loved that car, and it was with me through a lot of major life events, so there was a lot of sentimental value wrapped up in it. Ultimately the trans dropped 3rd gear, and it was time for it to go. I would have kept it, but I lived in an apartment at the time and there was just no reasonable way for me to fix it. Had a '01 Z51 C5 Vette that I bought with super low miles and in mint shape. Truly hated the car, but kept it for about 3 years, hardly ever driving it. Had a Stinger GT2 for about a year and a half; only car I ever bought brand new because at the end of 2019 they were leaving a pile of cash on the hood and I got it for $10k under sticker. Good car, but somewhat boring. Had plenty of other unremarkable cars, nothing that ever quite ticked all the boxes.
Now that interest rates are through the roof (and I'm not quite at the point in my life where I can buy a $60k+ car outright in cash), I'll likely be keeping the X5 for a while. It doesn't hurt that I think it's an excellent car
