1. what will JJP use with WOZ ?

Probably also some surface mount - not sure how that effects the discussion here though.

2. if the replacement cost is low from Stern/Sterns agents for these computer boards, does that make it OK to go with the design of the boards they have, or is this just a cost cutting exercise.

Massive difference - a 10 cent common component will be available for a long, long time, long after Stern stops making a specific board. Once day a game become an expensive boat anchor for want of a tiny problem that can't be fixed, and any Stern replacement boards costing many time their value due to rarity. No thanks.

3. If the current design of a Stern is well made, which looks the case to me, is it fair to say most items in a home market environment will last 10 years. Therefore, is it only the operators who shld have the occassional hassle ?
 

I have 20, 30 and 40 year old games that are perfect. And can be kept perfect because they are repairable. That's the problem we are discussing. If you are happy to scrap after ten years, that's fine then.