27/09,
I do agree with you in regards to the possible confusion that can result from the use of multiple waypoints in a RNAV approach, however they exist to allow for multiple points to join the approach from and to provide a definitive FAF point which is also programmed into the GNSS as a cue to conduct its own RAIM check and to transfer to tighter tolerences in RAIM and CDI display.
An advantage of LNAV/VNAV and LPV approaches however is that vertical guidance is actually provided thus helping reduce the workload in maintaining a correct approach profile (though you will still monitor that the information being displayed is still correct).
Also judging from a quick look at RNAV charts from the FAA, there is no difference in regards to the waypoints due to the approaches being designed to allow for LNAV, LNAV/VNAV and LPV to be flown from the one chart and to account for the fact that the correct criteria may not be met for the more restricive minimas, for example:
http://aeronav.faa.gov/d-tpp/1309/05050R21.PDF