Hi Jason,
Limiting the discussion for one moment to Australia, as a rule of thumb,
inland sites tend to be more favorable observing locations.
As you are aware, Australia in geologic terms is very ancient landscape.
As a result of its current position within a tectonic plate, it does not get
the uplifting forces that create the giant mountains that tend to occur where
the plates collide. What mountains there were are eroded. With regards
large professional observatories, high altitude is an extremely important factor
and for this reason it is unlikely we will ever see more large optical observatories
built on the Australian continent.
Whenever a 'not to be missed' observing event comes up, if it can be observed
from inland, then one tends to have a better chance of seeing it simply because there is
less chance of cloud. The interior of Australia is not desert without good reason.
The green fringe found down the east coast, where most of us live, tells us a lot
about the relative rainfall compared to the 'outback'.
One downside of viewing from far inland locations can be heat, which affects
both the seeing and mirror cool down times. A tradeoff is to find a site at
altitude that is away from the coast and south of the Tropic of Capricorn
and this is what makes, for example, Siding Springs and Mount Kaputar
great observing locations, but still far from ideal.
Extending your question to a global scale, some of the best observing locations
in the world are atop Mauna Kea on the Big Island in Hawaii and at places like
Cerro Paranal in the Atacama Desert in Chile and La Palma in the Canary Islands.
All these locations are remarkably close to the ocean, but their high
altitudes e.g. Mauna Kea is at 4200m and Paranal is at 2635m and La Palma is
at 2300m) puts them above most of the weather and combined with
their unusual terrain and other distinctive local meteorological conditions, make these
some of the driest places in the world.
For professional observatories, the deeply red shifted objects, which are often the
most interesting to cosmologists, can extend into the infrared and one problem with
water vapour is that it is opaque at infrared wavelengths.
For the visual observer who is lucky enough to take a scope to these
high altitudes, personal physiology comes into play and the lack of oxygen
can impact upon visual acuity and undoubtedly brain function. Not to
mention the all too common splitting headache one can suffer without
adequate acclimatization, something that could put a real damper on what
otherwise might have been a great night's observing.
For Australians,
without getting on a jet and flying elsewhere in the world where there are high
mountains, it is not a dilemma we face.
