There is a valid reason why you would make enemies stronger and not make more of them spawn. Basicly it comes down to alpha damage.
- one enemy with 100HP does 10 damage a turn
- two enemies with 100HP do 20 damage a turn
- one enemy with 500HP will do more damage over multiple turns but still only 10 damage a turn
if you would put to many enemies on the field at the same time, they could alpha your chars down in one turn. While if you make the select few stronger the fight would go on for longer and they might get the upper hand in the end, but you wouldn't lose from the get go.
As for spawning more , that shouldn't be to hard if DOS works more or less like NWN in regards to spawning objects from a template. Haven't looked into it yet, but this can't be hard.