In the UK the Live connection supplies current from the sub station and the Neutral is there to return it.
It would be very nice if you guys could all keep it like that! That is the intended circuit. No, don't do anything else.
At the sub station the Neutral is connected to earth. Now if your neigbour (on the same phase) is using 1000A then the resistance of the wiring between his Neutral pin and the connection to 'Earth' will develop a voltage that you will 'see' on your neutral pin. That's Ohms law. So Neutral isn't at the same potential as Earth - necessarily, it could be, depends on the current you, or your neighbours, are drawing. So, in the UK some other nutter can make your Neutral very high!! (normally though the wiring is so thick that they don't)
What is Earth for then?
Firstly it's there to distribute charge. My neighbours had their metal gas pipe changed for a plastic one and the dopey workmen reconnected the houses 'Earth' to the new PLASTIC gas pipe. As my neighbours activities in the house generated static they would find that they got nasty shocks from metal and water pipes in their house. The 'Earth' wire, properly re-connected then allowed this charge to flow to the 'Earth' - and literally cover the earths surface. The Earth, being a little bit larger than their house, spread out the charge so much that the potential was effectively zero.
Secondly 'Earth' protects you from being electrocuted - well provided that things are connected correctly! OK, so imagine you have a metal box with Mains Wiring in it and the Live wire disconnects and touches the metal case, which is 'Earthed'. Using just Ohms law we can see that the large current that flows (before the fuse blows - hopefully) will attempt to raise the potential of the metalwork with respect to, well, the 'Earth' you are standing on. Should the metal casing and eath wiring have such a large resistance to 'Earth' that the potential developed gets to above 50V (I think) - you will FEEL it!! So, if you keep the resistance between your metal box and the 'Earth' around you to milli ohms - then you will be able to tolerate 100s of amps of fault current before you can 'feel' it (read 'die from electric shock'). Note that it's not the potential that the metal box gets to with respect to the sub station - it's the potential relative to the Earth you are standing on that is important!
To answer your specific question - yes of course mains leakage current will flow back to its source - That's ohms law. Don't think that current flows in wires just because humans have printed words on them!! If current can find a path - it will use it!! (Did I mention Ohms Law?) Naturally the Neutral wiring will have a much smaller resistance than the Earth route so the currents will flow in the same ratio as the resistances.
Considering the two different resistances of the wet/dry Earth route and the Neutrals copper wiring, I would assume that the earth 'spikes' are there for the static reasons mostly (includes lightning) since it doesn't matter how big a spike you drive into the ground - the resistance presented to the sub station will largely depend on how wet the ground is and the distance to the sub-station.
Finally - try not to think of any such thing as perfect 0V, chassis, common, ground, +15V return, etc, etc. Ohms law says that if you have a current and a resistance - then you get a voltage. I bet that every point you would call 0V has some potential relative to anyone elses '0V', chassis, common, ground, etc. If you connect a 'charge' to the Earth then the charge spreads out evenly across the planet - that spreading reduces it to a very low potential since the 'Earth' is massively bigger than your house- but NOT zero, at least not while we still have thunderstorms!!
James