> The power resistor technique has the downside of... 

It's also the downside of using a linear regulator. They don't
adapt to their environment as switch modes do, as can be
seen from the wattage generated from large voltage drops
for example. For a one-chip circuit like the OP's, a SMPS
might be overkill though

> adding resistance to the power supply, yielding dips during
> current pulses, etc. May or may not be an issue

That could be mitigated with steering diodes and reservoir caps

> Also at low currents the regulator will see nearly 24V, not a
> problem for heat-wise, but does mean the regulator has to be 
> rated for 24V.  With a zener you'll always get the drop across
> it, so you can use a regulator with a lower voltage rating

The 78L05 has a 30V rating so that's not a problem. If an LDO
was used then you'd have to pre-regulate, as many of them are
much lower than 30V input ratings

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