I last replaced them with the plugs about 4 years/60-70k miles ago. I bought platinum plugs I if I remember correctly, so I still got some life on those. The car (2001 Buick Regal) is still in good shape just due for a tune up, so if the wires are due to be changed I'll add those to the list.
According to the 2001 Buick Regal service manual (PDF) spark plugs wires should be inspected at 100K miles, and replaced if necessary (p. 7-15).
spark plug wires should last a very long time, so just check them when you get the plugs done, and replace if they're worn out.
wires don't really wear with distance, it's time and heat cycles that cause the insulation to eventually degrade. usually there good for several years
look for cracking of insulation, particularly at joints. check for corrosion of terminals and if you're really motivated, check resistance (lower is better)