Scroll saws get used in very predictable ways most of the time. Intricate cuts on thin material. All blades have a working lifespan and as those teeth start to get dull the quality of the cut starts to suffer. Next thing you know you are discarding a blade that has a dull spot in the middle but fresh sharp teeth above. That irritated me and I was determined to get a little more life from my blades.
Use some sort of 3/4 inch material with a smooth hard top. If you are going to use regular plywood sand it carefully and give it several coats of hard paint. Sliding on just bare wood is hard work and results in ragged, jerky cuts.
Cutting the slit rather than drilling a hole means that I can quickly slip it on and off w/o having to take a blade loose and thread it through. In seconds I can have the top on an make a cut.
By making the top out of some scrap I have no money it it and that laminate on the top is actually a better surface to cut off from than the original table itself.
I find myself using it more than expected, slipping it on when I have a delicate cut to make and want the smoothest line and sharpest teeth.
I tried making a 1/2 plate in order to keep more depth but you were still using mostly old teeth and the 3 or for fresh sharp ones brought into play did all the work dulling quickly.
I am telling you this is one of those things that is just worth doing, you will not regret it.