You said you refused to install wheel spacers but installed strut spacers in the front. I do not know the difference really. Why ok on one and not the other?
I'll try to explain.. but basically they are fundamentally different when you look at how forces are applied and the possible ways they can fail.
A strut spacer is simply a shim that sits between the strut/spring top and spring bucket/perch in the frame. In my case it is 10mm, which is short enough to still use the original studs in the spring seat, going through the spacer then into the perch as stock, with plenty of bolt still through the nut. These spacers sit in compression only, meaning it is just a chunk of metal getting squished all the time. For this to fail you'd have to put EXTREME forces on the truck.. ones that would make many other things fail first. A more likely issue with this setup is the top of the strut moving downward 10mm but no adjustment to the bump stops which act on the lower suspension arm. If that 10mm is enough to let the strut bottom before bump stop contact you could damage the internals of the strut, but as far as I can tell this isn't an issue. Toyota seems to have designed enough travel into the strut to allow for the 10mm different mounting position.
Contrast that with wheel spacers. As stock the wheel studs are designed to thread into the lug nuts a certain amount. These are blind lugs where the stud goes into the nut, but not all the way through. Good engineering practices mandate that there is more thread engagement than is actually necessary, so in theory you could run a thin spacer and reduce thread engagement, but you are eating into your engineered overhead, and it would take.. an engineer.. to determine how much is ok before you start compromising the strength of things. Plus you can run into concentricity issues when a weel is hub-centric, leading to a wobble. All of this is on top of the fact that a spacer moves the wheel outward and as a result puts more force/leverage on the hub mounting face. So in effect you are changing the forces the system sees, and one could make an argument that you should want MORE thread engagement in that case. And this is if the hub is ok with the forces, which apparently they are. Toyotas in general and landcruisers in specific are over-built.
That's a thin spacer. Most people running spacers are actually 1"+. Suddenly there isn't anywhere near enough stock stud to move the wheel out and have a lug thread on, so the thicker ones bolt to the hub face and stock studs with their own lug nuts, then have a second set of studs anchored in the spacer that your wheel bolts up to. You are drastically changing the forces involved (unless you use a wheel with an offset that keeps the tread in the same place in relation to the vehicle), doubling the number of lugs that can work loose, increasing the likelihood of concentricity issues, hoping the spacer manufacturer uses the same standards toyota does for stud strength and mounting.. basically it changes forces a lot and adds a ton of variables. As for what's different with a strut spacer.. your wheels bolting to the spacer itself, no longer the hub, and the spacers are not just in compression. They are also in tension, and shear and all kinds of other dynamic forces are applied.
I've written before about how I'm impressed by toyota's engineering of these vehicles and like thinking through why they designed things the way they did. I put a lot of faith in their ability to know what they were doing, and personally wheel spacers seem like too big of a departure from the design parameters they used, so I won't be running them.. I'll use a wheel that has the correct offset, load rating, size, and weight to get the job done without having to put what I consider band-aids on a problem. And by the way no offense to the people that choose to run spacers.. many of them are quite smart and know what they are doing. I just choose not to.
Edit: and if pictures help I can find some.. but it'll take me a while as I'll be busy for a few hours.
