IMHO, comparing downtown Regina to downtown Saskatoon is apples to oranges.
Regina's focal-point is Wascana Centre (and it lives up to this - it's a destination. Look at Wascana on an average day - summer or winter, rain or shine - there are always people/activity).
By its very nature a city's downtown will always be a focal point, the degree to which it draws depends on the city's other activity hubs.
The vibrancy of Saskatoon's downtown benefits from the river flowing through it (as do most cities with a DT body of water). I think people are drawn to water & natural urban settings. This creates a bit of a self-fulfilling prophecy: people are DT enjoying the natural surroundings, so businesses, recreational & cultural facilities choose to locate near these areas. More amenities, and a sense of energy/activity draws more people. In turn, this draws more amenities....
If we were to shift downtown Regina to the area around Wascana, I think we could be on par with Saskatoon... but moving DT seems unlikely
In the absence of this, more pubs, restaurants, condos, apartments, theatre, etc DT will assist in drawing people, but I don't think we'll ever have the "feel" of DT Saskatoon.
Interesting to note that Wascana Centre has a distinct lack of business amentieis & it still draws crowds.