You are still missing the point (except Chilli). The engine fund is taken from the per hour costs and covers wear and tear that has ALREADY occured but you have not yet had to pay for. It does not exist to meet future bills.
So a share is worth a percentage of the airframe value.
Look at it like this: A new engine is £10,000 with 2000hr TBO. Thats £5 per hour put away for wear that has ALREADY occured. The engine fails at 1000hrs you have £5k in the fund that pays for those 1000hrs that were used. The group members split the outstanding £5k and it all starts again.
You don't pay into an engine fund in advance of flying the hours you pay into it after the event. So you should not expect to value a share based in what is sat in the bank raised to cover wear that HAS happened.
If you are buying into a group with no engine fund then the share is worth less than the market value of the aircraft divided by the shares as you are taking on greater risk.