Regarding the lack of PAPI/VASI:
In many European (Continental) states, it was common, until a few years ago, that if there was an ILS there were no PAPI/VASI's as back up. So, when the ILS was on maintenance-u/s etc. it was mark 1 eyeball and consumate skill, once again. There certainly was no effect on the use of the runway.
AMS was one of these airfields, but now it has PAPI backups. Whether this is no a JAA requiremnet I do not know. Germany was another country that had no backups; I'm not sure the situation there now. Thus I wonder if the preceeding comments about dispensations etc. are under FAA (or other) rules?
In UK it was reuqirement of base training and the type rating test to fly an approach without visual guidance. An excellent exercise that every pilot should be able to do. Given the number of airfields in European tourist destinations that are regularly used by many charter a/c of every type, and which have no ILS, only non-precision and PAPI's, it is essential to be able to fly an approach with mark 1 eyeball. Either the PAPI's could be u/s, often after violent TS's. or uncertified awaiting flight testing, or just on maintenance. To maintain the schedules the runways have to remain in use. It has been the case at some fields where the G/S was 3.25 and the PAPI's 3.00. Odd but confusingly true.
I was always taught that if there is a discrepancy between electronic and visual aid G/S, fly the electronic one. However that could be wrong due interferance and you should be able to ascertain that.
One things for sure with PAPI's, 4 of any colour is no guidance, especailly green; cos then you are very low!!!!