3M tape is finicky to use; if the surface is perfectly clean and you use adhesion promoter and you apply constant pressure and the temperature is good, it will hold just about forever. But if any of those isn't quite right, there can be issues. Also, it doesn't really like temperature fluctuations nor push/pull motions after it's installed. By that I mean, if you wiggle it enough, it will eventually let go. I used to own a company that manufactured interior dash kits and we used a ton of 3M tape, that's how dash kits install. So I've had a lot of experience with this stuff and having to warranty kits when the tape didn't hold, etc.
It's not a great solution for a lip spoiler in my opinion. I'm surprised that's Infiniti's solution for this. BMW uses actual glue to hold their spoilers on, it's called Betalink and once that stuff has cured, it's very, very hard to get the part off. So either glue it, or use screws and washers. Even regular screws won't hold forever, eventually they will pull out due to the forces the spoiler sustains from wind and such. On my BMW, I installed a carbon splitter and used bolts and washers to install it (hidden). I used 3M tape to hold it up while installing, and considered not bolting it in, but tested it by pushing on the splitter and the tape let go pretty quickly.
