You've inspired me to think about this...here's my suggestion:
Note that in my vision, Barrington turns into Upper Water just north of the sewage plant. The street then travels around the perimeter of the dockyard land, casino, Purdy's Wharf buildings where it forks southbound onto Hollis, and from Lower Water northbound. This would be the primary route into downtown, with Lower Water being made one-way the entire length.
Barrington Street would pretty much travel the same way it does today, although it would intersect with Upper Water just north of the sewage plant. Provo Wallis (the street that goes into the Dockyard) would be re-aligned to create a four-way intersection with Barrington and Upper Water.
Cogswell would continue down the hill intersecting with Barrington, continuing on to terminate at an intersection with Upper Water where the casino parkade entrance is.
One interesting thing that could be done is removing that silly pedestrian mall on Granville and continue it along to terminate at Cogswell. Or it could be maintained as a shopping street, with street-level retail along it from Duke to Cogswell.
I think there's one thing we can all (hopefully) agree on: Hollis and Lower Water have pretty much become the primary downtown throughfare, so it just makes sense to continue Barrington onto those two streets somehow. This meets that criteria, while also maintaining easy access to Barrington and Cogswell streets. I see Barrington as becoming either more of a local street, or having some sort of public transit component. The only problem I see with my vision is that Spring Garden terminates on Barrington
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