Well - spark plugs always arc - that's how they work
On a more serious note, I haven't looked under the hood of an 01, but if you have spark plug wires instead of coil on plug, and the wires are old, with embrittled/cracked insulation, etc. you can get discharges in the insulation (no big arcs, though - certainly nothing you'd see while working on the suspension...)
OK, in summary... the 01's have a coil system and not spark plug wires. So it's not possible to have "arcing spark plugs"?
We took the van to the dealer for an oil change and inspection since it's coming up on 105k miles. Aside from the big timing belt service, the van's in good shape. So that confirmed my suspicions and your warnings.
We've canceled any scheduled service and won't be returning to the other shop (we've only had them give estimates so far). I have a trusted shop that will do the timing belt for us in a few weeks (we tried the shady shop because our normal shop was booked solid for several weeks).
You can get arcing with plug on coil. the coil packs have a boot that wraps around the plug just like a spark plug wire has a boot. Those boots can crack and "leak" spark energy to the head. See the section called "COP Checks" at this link: http://www.aa1car.com/library/copign.htm .
You can replace the boots on some units but I couldn't find boots for our application.
That said, I'm not sure how they came to that diagnosis. If they hooked the van up to a diagnostic tool that can perform spark balance tests, they would have been able to see which cyllinders, if any, was showing a fault. If misfire codes were present, they might have concluded this was the cause.
It is obvious that the shop did nothing of that sort.
How many shops that you know would do all that without charging a dime?
I will bet the shop did not even remove the top engine cover to give him that "diagnosis". For crying out loud, he was not told the specific plug which was arcing, implication being they all were arcing.
P.S. Changing timing belt can be pushed out by few weeks with no harm. I presume your regular shop would take you in immediately in case of emergency. If so, I would not give timing job to another shop. Keep good relations with the trusted shop.