now now, i beat the snot out of my 03 zr2, it has had strut extentions on for more than 2yrs now and the only issue i had was getting them on! they will never come of and have yet to snap. however, that said in the future when replacing the blown struts i'm still running i will purchase the spacers!
I've seen photos (one has been posted on this site periodically) of two that have split. You and 99.9% of the other users may never have it happen, but that's one failure that, if it should happen, could cost a life.
I've not been able to justify that myself for 1.5" more droop.
Quality spacers, on the other hand, don't (to my sensibilities) add significanly to the front suspension's risk of catastrophic failure.
For a low-speed, off-road only truck, extensions make perfect sense. For a daily-driver, though, no thanks. Spacer me.