While tunneling would be nice to have, I don't see it near the importance of reconnecting River Market/Columbus Park to Downtown.
The grid is mostly intact over I-670 and connectivity isn't hindered. I think most would be comfortable to make relatively short walk over, given the large sidewalks and barriers.
Over I-70, on the other hand, the gap is large, especially Delaware bridge, sidewalks are skinny and barriers are minimal.
The ability to turn this land into something that generates money for the city, instead of significant cost with no end in sight, seems like a no-brainer.