While making Showcase a 12 issue mini-series every year didn't exactly make it appear terrible, it gave the comic a slight sense of shaken continuity. I realize that the stories have always remained without continuity with the other stories that came in previous and upcoming issues, and that continuity didn't really matter at all in this comic, but making it a mini-series somehow took some magic away from the overall effect.
My idea has always been to turn Showcase into a monthly comic featuring different creative teams and characters with different stories and still keep it all in DC's continuity. The coming of the DC PLUS line is exactly what Showcase should be. Fantastically written, well drawn, and overall fun stories all for the sole purpose (other than profit of course) to have a reader enjoy it. Showcase seemed to crank out one bad issue after another hence low sales (I'm making an educated guess there) and cancellation. If Showcase had been turned into a monthly title and had the quality of it's final issue (Showcase '96 #12) and all of the PLUS issues every month it would've been a hit.
I would think though that if DC would now try to revamp the Showcase title into a monthly book with the quality and fun of the very first run it would be a hard thing to do. Since the book has accumulated low interest, readers may have the opinion of "what difference would the "new Showcase" be from the old mini-series?" floating around in their heads. It might take a greater amount of advertising to restore it's classic feel than say - if it was the same idea but with a different title name. Maybe the seemingly successful PLUS line's title would fit nicely. Even with a title carrying less doubt from the readers though (PLUS), the classic feel of DC's original Showcase title would not be there as heavily.
Another point is to only have one story in an issue. Whether it continues over into the next issue or not doesn't matter, but having only one story in an issue would give the story more space to work with and allowing for more character development.