Waze's assets are both its map and its community. As for the community - its value is estimated based on some rule of the thumb, calculating expected revenue from advertising etc. Yes, each and every one of us is worth $5 and it quickly adds up.
The other asset that Waze holds is its map. After 3 years of work there are patches on the world that have an exceptional good map, so good that its usability is better than any commercial map. But really - most of the map worldwide is still unusable. It will take many more years to get those areas in a shape where you can expect a useful route.
Online communities can fall apart within weeks or months, history shows that selling the ownership/changing tactics can accelerate that process. Waze's community - held together by 0.1% of its userbase - seems exceptionally brittle and it does not really help that 2/3 of us are on Android.
If Apple wants the map but looses the community in the process they are in for a few unpleasant surprises. They must keep the community alive if they ever want to harvest the maps, and Apple has a notorious bad reputation with social things. On the other hand it is understandable that Waze would sell; getting offered 300 times last years revenue is more than many of us could withstand.