Besides sunlight, smoke is something to best avoid. As is high humidity and moisture. Many speakers which have foam surrounds can easily have the surrounds replaced, it's not automatically a death sentence. And depending on the brand, it's probably best to replace the caps in the crossover every couple of decades or so. Large woofers should be rotated 180 degrees every couple of decades as well, if possible, to prevent stresses on the suspension.
Among my loudspeakers is a stock pair of 1977 Klipsch Cornwalls that sound excellent thirty-three years down the road. I have a pair of Pioneer CS-99A, with the cambric surrounds, from the same era in great condition. I also have some raw drivers from the 1950s that seem to work very well and friends that use Altecs from the early 1960s that sound pretty good.
Heck, there are guys using Western Electric and Klangfilm speakers from the silent motion picture era between the wars, and loving the hell out of them. I would not sweat it.
http://www.audioanthology.com/audio1.html