Is it viable to use cottered cranks? I'm restoring a Bianchi Sprint (~1975).

It has a cottered crankset/bb. I was originally planning on replacing them, because we all know that cottered cranksets are junk, right? Well, they have a great Q-factor and the rings I want (52-42, because it's got DT shifters), so I'm looking at trying to make them work.

I know cottered cranks are gone now because square taper is a better, lower maintenance, more foolproof system. But that doesn't mean that cottered cranks can't work well, right?

Is it going to be an ongoing nightmare trying to keep these cranks working smoothly and silently? This bike would be used heavily (~100 miles/week).
Give them a try. 

The main reasons they used to fail, if my boyhood memories are accurate, was incorrect installation.

When installed firmly they would last for years.

The important thing is proper support for the bike and pedal arm while installing the cotter pins. The pins must be hammered in firmly, without transmitting any of the hammer impact to the BB bearings. Destroying the bearings was common. After installing the pins firmly the nut on each should be tightened to hold them firm. 

If you have a source of the correct cotter pins then trying will not cost much. If you find them to be too much trouble then you can always such to plan B: a square taper BB.

The Spirit crank and chain rings were integrated, so you'd need new rings of you replace the BB.