You might not use your car on a schedule, but if you aggregate thousands of private vehicles you can build a statistical model that gives you pretty high confidence that a certain amount of charge will be available.

Yes, the fraction of total charge that you could plan on being available this way is going to be a lot smaller than the school buses, but there is a lot of electrical energy available in EVs so even a small fraction of it is a big deal to grid stability.

Furthermore, a lot of the potential for EVs as grid balancers isn't for the day-to-day variations in supply/demand - it's for those few hours a year of demand peaks, and in open electricity markets the wholesale price of electricity goes to pretty crazy levels (thousands of dollars per megawatt-hour depending on the market design). Those few hours of crazy-high prices pay the costs of peaking generation that only operates at those times.

In Australia, the market is capped at $15,000 per MWh. Say you configured your car so that it would sell back into the market only when the market was above $1000/MWh.

In one winter month I looked at, applying these rules you could make about $60 from a total discharge of about half the car's battery capacity (and not all of the high-priced period was contiguous).

That sounds like adequate compensation for fairly minimal degradation of the battery capacity.