Either way something should be done, one of them at least, ideally both.
Although it is only 400m from Central Station, the station forms a huge urban impenetrable wall that isolates Stephenson Quarter. What is 400m as the crow flies is actually a convoluted and unclear route via Centre for Life or Orchard Street underpass. Bear in mind Sunderland Central-Park Lane-University is around 350-450m apart.
The once proposed southern entrance to the Station would be ideal. The recent Central Gateway plan by Network Rail is an exercise in fleeting around the core issue, and still substandard in terms of a direct southern approach, but we are likely stuck with it- hence an idea for the Metro station, seen as the North East LEP is pressing (with presumable futility) for an expansion of the Metro.
Now, as well as providing an essential boost to a critical city centre development (looking substantially more appropriate and exciting with Igloo on board) a Forth Banks Metro Stop could serve as a public transport hub for the emerging 'Quayside West' developments along Pottery Lane all the way to Calder's Yard. Not to mention serving the far end of the Quayside. Could imagine some external escalators giving pedestrian access to the Quayside itself and help rejuvenate this dead part of town West of Copthorne.
Having a station platform as well on the end of the QE2 bridge would be suitably spectacular, and very Newcastle.
It'll be about another 20-25 seconds until it stops at the 'Stephenson Quarter' station, which is a huge difference if you're walking to it.
That said, the diversion around the Centre for Life isn't actually that much of an issue - I worked there for quite a number of years in West One, and it was a bit of a schlep, but that was mostly due to the steep gradient of Forth Banks. When I worked there people never complained about the distance to the station, but the subject of the steep incline did come up - mostly in winter when there was snow or ice. A south entrance that could also serve as a thoroughfare would be a far more effective use of any money, as it will also connect the area to the rest of the city centre far better than a station would.
The landlords of West One and the adjacent Forth Banks Tower have struggled to ever get the buildings anywhere near full occupancy for the commercial units, as companies don't want to be there - they prefer to be closer to the actual centre of the city. Being on the outskirts of the city centre is seen from a business perspective as a bit of a cheap cop-out. The rather crap quality of the buildings doesn't help with either of these things though.
For the west quayside area to get any substantial uptake in development will take quite a bit of effort, and I'd say you'd be better installing public escalators or lifts as others have mentioned than a station, as the issue for many is the steep climb up into the centre of the city rather than access to public transport.
In the case of Sunderland - Park Lane, there is a very big justification for this closeness between the stations, in that both serve the city centre, but one is the main railway station, and the other is a major bus interchange point. If the bus station wasn't at Park Lane, it's a safe bet that the station wouldn't have been constructed due to its' proximity to Sunderland. Even so these two stations are still about 100m more further apart following the route of the line than Central Station to Forth Banks would be! The distance between the platform ends would be somewhere in the region of only 300m! (For context, we have 60m long trains...)
With infill stations there has to be a very careful balance - it would be nice if everything that was beside the Metro route was within 2 minutes walking distance, but you also have to weigh this up against the effect on the end-to-end journey times and impact it has on the headway between services. If a train stops for 30 seconds at a station, you realistically lose 1-2 minutes due to braking and acceleration. If the stations are close enough that the new infill station stops the train being able to attain its' top speed that time now increases even more and on a busy section such as between South Gosforth and Pelaw you can start to affect the number of trains that you can run through the route.