Yea I was curious about gluing the upper fairing back together
It depends on where it's cracked. If it's the usual bit around the turn signals then glue generally doesn't work.
I found that plastic welding worked but is difficult as the plastic is quite thin there.
Once I got mine welded and shaped correctly, I then roughed up the inner surface and reinforced it with 2 layers of woven mat fibreglass.
For gluing busted parts back on, you can use a mixture of Acetone and powdered ABS or get some ABS/PVC cement.