This is a good subject and one many tuners have argued about for years in one form or another.

Its very similar to the question of how equally do you need to balannce the CR of each cylinder when modifing combustion chambers.

I personally don't think its much of an issue on 4 cyl engines as the transient opperating condidition of the engine will mask a fairly large variation on cyl to cyl outputs. Certainly in terms of wear it can't be an issue... if you think about it each cylinder is performing differemtly nearly ever time is fires anyway, as the revs and hence volume of air/fuel will be slightly different to the cylinder before it...

As for fueling and ware differences, if you take an A-series engine (mini) then the outer cylinders ALWAYS run lean due to the 2 port design... even tuned up to near 200 bhp/l there is still little evidence of excessive crank wear due to different power output per cylinder!

Just a few thoughts, nothing 100% thought through!

Alex