fohat is going to be so jealous.
I recommend swapping the spring between the spacebar and the Pause key or something. The standard spacebar weight on these is ridiculous.
That's ok, most of my work is xcriptio continua so I don't need the spacebar anyway

Truthfully, you are right, the spacebars on most Space Invaders boards are way to heavy, but I have found that after a short time I don't really notice...until my arthritis starts complaining. Of course upon, but returning to a more typical keyboard I end up hammering the spacebar.