Is it worth a proportion of a reasonable landing fee? To me, yes.
From the UK national careers website:
Job profiles. Firefighter. Hours. 42 per week. Starting salary. £21,157 + per year
.... with other fire services and institutions, such as the British Airports Authority, ...
If a full-time fireman earns 20-30,000 a year, we could use £50,000 as a guesstimate of how much it costs to employ a fireman for a year. I suspect this would be low, by the time you've taken into account equipment costs etc...
Let's say for the sake of argument that all ten of the firefighters are employed half-time, it might cost £250,000 to provide a fire service for at most 1900 movements (2004 figure) which would be £130 per movement.
You could argue about how this would be shared between Bigear's spamcan and the commercial flights, but either way I don't see how it could be incorporated as part of a 'reasonable landing fee' that I would personally be willing to pay. Even if I'm 50% too high in my back-of-the envelope calculation.