Yes, the copper plugs on these V10's should be replaced every 20K or so but i think the wires should last twice that.
I pulled the original plugwires off my 97 a couple years ago at like 42K miles, measured the resistance with a voltmeter and they were within spec. Replaced em anyway with a set of AB Quality wires that i had.(which had a measured resistance of much less.) I plan on these taking me to 100K and think that any premium set of wires should last more than 40K miles.
I think there might be a false assumption on these forums about our wires prematurely failing that was caused by some owners running headers without heatshields causing the wires to endure excessive heat. Its also possible owners in hotter regions that track their vipers could have less life in the wires. Chuck if you really are still using stock wires and replacing every 20K then go ahead and measure the resistance of a 20K set vs a new set and report your findings