You can get a tap for less than $25, and yes, it's a good idea. PM 4cznskier, he may have some for sale for cheap.
What the tap does is eliminate the possibility of the screw pulling/separating the metal layers or blistering/puckering the topsheet when threading in. By cutting the threads with a tap rather than "swaging" them with the screw, you get a much cleaner hole. A big bonus, to me, is that you can very easily gauge the tightening torque when putting the screws in. They go in very smooth (with a little glue to lube the threads) and gently snug up against the "stop" point (which I follow with a brief 1/16 to 1/8 turn to fully snug them, and then walk away). When you don't tap threads, you know it's a bit of a bear to drive the screws in, and you lose a lot of touch/finesse as far as torquing down, when to stop, etc.
I even tap skis without metal layers, because I prefer the overall experience. I really like the increase in control, and think it results in a cleaner, nicer mount.