The Alfa twin spark (wasted spark) system is a pretty rare thing in general motoring.
Most spark plugs on other marques last around 24,000 miles at best before bad running issues develop and even then, cleaning rarely helps as the electrodes are all but burnt out.
Due to the wasted spark system, the Alfa Romeo plugs are designed to last up to 60,000 miles, they are very efficient at what they do... It is extremely rare that any cleaning actually helps, you may get 1,000 miles or so out of them after cleaning but it won't last long before issues come back... You end up developing further issues with carbon build up due to unburnt fuel and lower chamber temperatures can eventually move the issue further along to cats and O2 sensors clogged and coked up... So it makes far more economic sense to replace them straight out.
In all honesty, I have never had a spark plug in a TS or Busso V6 fail prematurely so when they do start to misfire, it is time to change ASAP, It is usually the coil packs that give up first and their rubber boots causing arcing ...
Saying that, if serviced on a recommended basis, there should be absolutely no reason why a spark plug would cause a problem, they are usually changed well before that has a chance to happen