I've thought of an idea:
Use the 100 point scale still. At the end, average the total points per player by however many maps they speedran. And then provide an additional point bonus for each map they did speedrun.
That is really bad as well, cause then sending in a bad time could potentially give you less points than not sending it in, that shouldnt happen.
If you really wanna change it just do something like 1000*0.75^(your place). That way the point difference between 1st and 5th etc. is big enough to potentially make up for a missed map.
To be fair, the system works fine if everyeone submits 5 demos, that was pretty obvious from the start. So everyone who didnt submit demos just doesnt seem to care enough.