If all signals are adjacent to ground (not power) planes on both sides
of the connector, then it is better to keep them adjacent to ground
pins through the connector.
Replacing ground pins with power pins would force some of the
switching return current to get from a ground plane to the power pins
and back to a ground plane again. You would need to add capacitors
around both sides of the connector to try to minimize the effect of
such discontinuities on your signal paths.
On the other hand, migrating power from ground pins does increase the
loop inductance of your power system at the entry point to the board.
Use good supply decoupling.