No need to use bolts for the cunningham fairlead or the Clamcleat if the screws feel tight in their threads. The same goes for the block plate; the cleat plate is off-axis loaded from different directions practically all the time, so you might want to bolt it if you already have access to the backside. Even then you don't need big backing plates or oversize washers. Those fittings aren't among the first to fail on a Laser.
RE: Fender Washers
In my experience (I own a 1979 and have worked on numerous boats of similar vintage), the block of plywood underneath the laminate is usually wet and spongy. Some people use longer screws and like other reinforced points on the boat, the screw going through the wood and the inside laminate will offer more resistance and thus feel tight. It may not fail, but if you are putting the effort into thru-bolting, for 50 cents more, you will avoid potentially pulling the inner and outer layers of glass together.
Putting in a hatch is easy and thru bolting on an older boat a good idea.
On my 1978 one I had the cunningham on really tight (it has the original rig) and was landing on a lee shore in about 15mph, undid the mainsheet, blowing in nicely and as the boom swung around over the front of the boat it really loaded up the cunningham and the fairlead came out with quite a bang!