Your car's now 13 years old w/~90k miles. A bad O-ring's no big deal, but a cracked or broken tube can be a big PITA, maybe even costly. The physical properties of almost all thermoplastics (in a former life I was an engineer in the plastics industry) will degrade with extended exposure to heat cycles. The tubes have been known to fail, which is presumably why you asked the question.
Why risk having a potentially costly failure at the wrong time when you can quickly and easily swap out all the o-rings and tubes for only $75 bucks while you're in there installing the plugs? Excellent, EZ to follow instructions at
http://www.pedrosgarage.com/Site_3/Change_Spark_Plugs_%26_Tubes.html
BTW, I agree w/BudmanV24, stay away from exotic or "improved" plugs. The OEM Beru's are fine, if a little pricey (I'm happy with them); the Bosch plugs Pelican sells for $4.50ea are good choice as well. Pedro's got part numbers on his plug change DIY article should you want to buy local.
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