There are incandescents that have heavier filaments or are rated for higher voltages. These were designed for vibration areas and inaccessible areas. They do put out somewhat less light because of the higher resistance filament. As you said, more heat less light.
The long-life lightbulb is just a myth. You either have a light bulb or you have a resistor, they only meet one another at a certain point of usefulness.
That's what I thought. IIRC, there is tungsten inside and over time it ablates off and deposits on the inside of the bulb. That's the dark discoloration which occurs in the bulb. The more robust you make it the more it shifts the spectrum to IR, and so on...
Filament boil-off does decrease the light output as well. You're right, that's the dark-silvery coating on the inside of a bulb, that's metal that's boiled off the filament. It's a neat effect, but not a useful one if you want light bulbs.
Little high-output bulbs are more susceptible to it. I assume probably due to the high drive levels and size of the envelope.
I've always wondered if the small 12V halogens last longer because the filament is thicker (has to be due to lower voltage, i.e. higher current).
I think the main issue is evaporation of the filament. It will develop thinner spots, which get hotter and evaporate faster, thus get thinner faster.
Halogens (and xenons) are unique in that they constantly boil and re-absorb the filament material due to the gas in the bulb.
They're really quite amazing and energy efficient, as far as a resistor that lights up goes.
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