I'm making a top-down shooter and want to scale the difficulty of the game according to what the score is and how much time has Passed. Along with this, I want to spawn enemies in different patterns and increase the intervals at which these enemies are shown. I'm going for a similar effect to Geometry wars. However, I can think of a to do this other than have multiple if-else statments, e.g. :

        if (score > 1000) {
    //spawn x amount if enemies
        }
        else if (score > 10000) {
    //spawn x amount of enemy type 1 & 2
        }
        else if (score > 15000) {
       //spawn x amount of enemy type 1 & 2 & 3
        }
        else if (score > 25000) { 
       //spawn x amount of enemy type 1 & 2 & 3
       //create patterns with enemies 
        }
       ...etc

What would be a better method of spawning enemies as I have described?