"What do you think will happen to the price of Platinum (or iridium, or anything) if you start shipping it in in 5,000 tonne lots?"

Price of Platinum will lower significantly. South Africa and Russia won't be as happy?

"The annual worldwide production of platinum amounts to some 160 tons, compared to about 1,500 tons of gold. In fact, in order to produce just one ounce of platinum, about ten tons of ore must be mined."
http://www.goldcalculator.com/index_files/page0036.htm

But I didn't go into a lot of detail regarding this subject. And wasn't suggesting one would produce 5000 tonnes per year- though one could see such levels of production coming from space at some time in the future.

"Only a few wealthy collectors will pay MORE for extra-terrestrial Platinum group metals, and THEY can be accommodated by Mining the K-T boundary layer for material. Most users will pay LESS for a bulk commodity."

Well, I'm not in the market for a lunar platinum ore paper weight. And as you say there are only a few who would be- but 1000 individuals of 6 billion people is very few.
You wouldn't need to be on the Forbes 400 list, but you would need to be fairly rich to be spending tens to hundreds of thousands of dollar on these kind of trinkets- and perhaps an oddball like a lady who owns hundreds cats. But someone like Bill Gates might be in the market for the paperweight- as an investment [of course] and if it looked really nice.

But yes it's really the Platinum group metals which is the topic rather than just platinum:

"The platinum group metals (alternatively, the platinum group or platinum metals) is a collective name sometimes used for six metallic elements clustered together in the periodic table.
...
The six platinum group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits."
http://en.wikipedia.org/wiki/Platinum_group

Palladium:
"Palladium, together with platinum and rhodium, are primary components in autocatalysts that reduce vehicle exhausts emissions of hydro-carbons, carbon monoxide, oxides of nitrogen and particulate. Autocatalysts convert most of these emissions into less harmful carbon dioxide, nitrogen and water vapor. Autocatalyst is palladium's largest and fastest growing demand sector, accounting for 49% of total palladium demand in 2006."
http://r0.unctad.org/infocomm/anglais/palladium/uses.htm

Palladium is currently lower $200 an oz:
http://www.kitco.com/charts/livepalladium.html
Graph of world production:

"Rhodium (pronounced /ˈroʊdiəm/) is a chemical element that is a rare, silvery-white, hard transition metal and a member of the platinum group. Rhodium is found in platinum ores and is used in alloys with platinum and as a catalyst. It is abbreviated in the periodic table to Rh and has atomic number 45. It is typically the most expensive precious metal"
http://en.wikipedia.org/wiki/Rhodium
And:
"Other uses

Rhodium is used as an alloying agent for hardening and improving the corrosion resistance[16] of platinum and palladium. These alloys are used in furnace windings, bushings for glass fiber production, thermocouple elements, electrodes for aircraft spark plugs, and laboratory crucibles."
And:
"Rhodium's typical historical price is about $1,000/troy oz,[19] but in recent years it has increased to about $4500/troy oz.In 2008 the price briefly rose above $10,000 per ounce. The 3rd quarter 2008 economic slowdown has pushed prices sharply back below $1,000 per ounce, however."

And I believe Rhodium is used in rocket engine components- assuming you are NASA and can afford it.

"Iridium spark plugs are fantastic. maybe everyone will have them, but only when the price comes DOWN."

Yeah, that would be nice.