I have a question about tilt/trim. Can trimming up the motor on a small horsepower boat say 35 - 40 hp while running WOT help gain speed on an engine this size. Lets just say the boat is a 16ft aluminum boat.

I have no experience with this, but if your boat will get on plane with the existing motor, then the physics would still apply when adjusting the trim.  However, improvement in speed may be marginal.  In truth, I just don't know.

Depends.

Trimming an engine up begins the process of bringing the bow up out of the water. Ultimately the process is complete when the entire boat hull is up out of the water with only a small portion of the back of the boat touching water.

Now, to your boat. IF your engine has sufficient HP to lift the front of the boat out of the water you will see speed gains. OTOH, if your boat is underpowered and you have a heavier boat with decking and lots of load, the engine won't create sufficient hp to raise the front significantly and you may see a decrease in performance as the rear end of the boat is driven deeper into the water.

Another problem you might experience is porpoising. This is the front to back pitching a boat does as it starts to raise itself out of the water and then falls back down.

Yes!

I have a 17' boat with a 40. While running I can adjust the trim and watch the MPH change on the GPS.