Got my boot lip spoiler I don't want to go attacking my boot with the drill yet though. For one, is it worth drilling or grinding the bolts off and just sticking it down? If I do drill, are there any templates around?

to be honest drilling or sticking only has cons for your boot!but i would stickerflex it(glue)and leave it a couple of days!
drilling = possible rust issues,plus gluing gives you some leway to ajust

im curently working on a trueno ae86 rear spoiler for my boot lid

Wouldn't at all go for just sticking it, it will fall off or come away at some point, especially as on the saloon it's quite useful for grabbing onto to shut the boot!

Bolt holes are easy enough to drill and measure up. You'll probably have to bend a couple of bits of metal out from the underside to get to the bolts within the bootlid. Make sure you paint the holes when you drill them out, and you wont have any trouble with rust. There's a template for the hatch spoiler in the blue books section, not sure about saloon though