Thanks for the inputs so far, please keep them coming.
Of prime concern is the cost of the upgrade, considering that the Mode C is working just fine. The other consideration is that we are going to change the radio (yes we still have one) to an all singing & dancing GPS type navcom on 8.33 separation. That's a bit of a sting.
Doing the Mode S at the same time seems logical, if money were no object. However, the money pits are not bottomless, and the old girl has some other repair/maintenance priorities to be addressed.
All I'm trying to do is to establish the priority ranking of a Mode S.
-Netherlands are now restricted to Dambuster style bombing raids at low level (watch for the pylons!)
-SOME London TMA remains accessible, ie to nominated airfields on the margins.
-The creep of EASA regulations will likely lead to its expectation. Charge the GA flyer, yet benefits accrue to the other users ie ATC and jets.
My query remains one of restrictions and access.