While I still go for bolts as well with larger pieces if your using adhesive that has maximum contact with the two pieces your effectively spreading any load across a much wider surface. Imagine a spoiler, 6 bolts, so the load on the spoiler is being spread over 6 points, if your exerting 6kg of force then each bolt is supporting 1 kg (assuming an even load which obviously never happens) that's 1kg on the mount points, (maybe 2cm square) with adhesive your looking to spread that 6kg over say 1 square meter, your exerting much less force on a single point. Most adhesive works from suction as well, once gripped and solid it's very hard to remove! It's perhaps not obvious when thinking about because you think the bolts are stronger, that's true but it's not the bolts that are the weak point it's your mounting points!