You bring up some great points, but let me answer them.
I have the Arbitron Winter 2006 report in front of me. The 12+ Hispanic estimate for Cincinnati is 1.3%. That's 22,000 based on the 2000 Census and projected ahead, but I'm fairly positive that's increased even more in 6 years.
WCVG routinely got 12+ shares in the neighborhood of 0.4 to 0.8 during its run as Gospel. I think that's about where the Regional Mexican format will be. With these sharply niched formats, it's not so much about Cume as it is AQH. You have to think that listeners will stick with the only Spanish speaking station in the market for long periods of time.
I also point to WDBZ's Sunday night Spanish programs that are locally produced. WDBZ gets over a 1.0 share 12+ between 7pm and Midnight on Sundays with a relatively small cume that mirrors the AQH. During most of Sunday, they don't break a 1.0 share 12+. During that Sunday evening period with Adults 25-54 (AQH), they beat WCKY, WKRC, WKRQ, and WVMX. With Women 25-54 (AQH), they actually beat WRRM during that time and it's over a 5.0 share. During no other time on WDBZ's schedule do they come even close to being that competitive. The Sunday evening daypart is way over their weekend averages. Now, that really is the ONLY time that Spanish language radio is available in Cincinnati, so you'd expect long listening. When it's spread out over the entire week and is no longer a "special" program, that listening will be diluted. But, I think the audience is there and it will be VERY loyal. (It's also interesting to hear the "Right Store. Right Price." Kroger jingle sung in Spanish!)
There are also rumblings that Davidson is interested in WCIN.