I'm sure a lot of pensioners are capable of catching a bus and then an onward tram or train, even if there isn't a tram or train stop near their house.
Regarding commuters if you had to pay to park at the station (or Metrolink stop), while the bus to the station becomes free will it attract those who 'park & ride' to leave the car at home?
Many, but by no means all, could connect with rail transport, but in practise, it would be pointless unless you lived a considerable distance from the city centre and the bus sector was only a couple of miles. Even then, its probably only worth considering for heavy rail. Most Metrolink running times are barely faster than off-peak buses, most Metrolink stops are devoid of meaningful shelter from the "elements" (and I don't just mean weather) and the same goes for bus stops. As things stand, all three forms suffer from poor punctuality, so it is often just as quick (and less hassle) to stay on the bus.