My vote is mainly on cost for the 11 Street car v. no car options - unlike almost every other project in the city's history, there's really not a convincing "need" for the vehicle access to be maintained here. Before anyone get's too excited in rebuttal - sure, it would be nice for car access to be maintained some specific routes and trips, but 11th is probably the least consequential road crossing into and out of the core for vehicles, on account it's really a short dead-end street, and has functioned with a train crossing for a century - it's simply not a major or important corridor for vehicles, nor has it ever been relied upon as one due to frequent train interference.
Due to the at-grade crossing both fire trucks and buses both don't "need" vehicle access here - again, they both operated as if this crossing didn't exist for a century. If closed to vehicles, nothing would change for their operations. If the fire department had an issue, they would have road-blocked the pedestrian-only option already, like they have on many previous road-narrowing and traffic calming projects. They didn't because the pedestrian-only option wasn't killed yet - that's our proof that fire and transit are okay without it.
So it goes to cost - if you can get a car underpass for the same price as a pedestrian-only one, go for it. If not, I don't think it's good value to add cars and the associated extra effort, depth, engineering and cost that goes with it. I get opinions are strong on this, but if there's ever a place where cars are more of a nice-to-have rather than a need-to-have project requirement it's this one. All the park stuff is a bit of distraction, it costs nothing in comparison to the grade separation but also isn't needed - a bit of red herring in all this debate IMO.
Most critically - if we do end up with the car underpass, we must avoid the very Calgary thing in over-engineering the hell out of it. a single lane, no truck access, no shoulder. Keep things tight, cheap and narrow so we don't bloat this underpass into yet another giant, expensive and redundant car circulation in our most walkable area that already has many better access points.