Let's start from beginning - WORLD 1 (W1).
It's quite important to pass through this map with maximum score. Good reason for building wealth towers, which adds you 30% more cash to every killed enemy. Of course, everything take place near crossroads. My succession:
1. build all 12 applied mushrooms (and let them stay on basic level)
2. apply elements combination to make 3 wealth towers closest to the centre of crossroads and upgrade them gradually to level 5
3. well at this moment, it's possible to finnish all other upgrades to wealth towers on level 5
It's simple and faithful philosophy! Commonly you can count with all 6 skill points.
But yet... Unfortunately, it has one slight construction fault - final enemy in batch of them all sometimes pass through... ;-)
Next lesson - WORLD 2 (W2). Sometimes...