What's the point of low idle temperatures anyway? Isn't it best for this kind of hardware to keep the temperature range as narrow as possible?

Any reason not to reduce idle fan speed so that the card is running 65°C(idle)-85°C(load) instead of 50°C(idle)-85°C(load)?

The only downside I can see is more radiant heat seeping from the card during idle, or is it detrimental to the longevity of TIM to have higher temps 24/7? On the plus side is less fan wear.

This PC is practically silent, but for this GTX 285. And if I drop the idle fan speed from 40% to 30%, that noise is vastly reduced.

AFAIK lower temperatures are good for longevity in electronic components and bearings, maybe even TIM, normal variation should be irrelevant in PCs. As a warning example: my LGA775 rig's Asus mobo control failed and didn't start up the rear exhaust fan, killed my EVGA 8800 GTS 512 that ran hot at idle.

Since yours is a 285, maybe it wouldn't be a huge loss if it were to die a heat death while you enjoy a quieter environment... afterwards you could get a card with a decent cooler.

Assuming it's a blower style cooler with some of the exhaust going out the back of the case...lower idle rpm will mean a few degrees higher temps for everything else (mobo, CPU, etc) and might also raise the idle power a few watts.

That said, replacing the 285 with a current gen card like the GTX 660 would reduce idle power by 35W, load power by 80W, and you'd have a quieter PC.