For Mayor Ed Lee, the big benefit to razing the end of Interstate 280 and redirecting Caltrain’s tracks into a tunnel through Mission Bay is all the land it would open up for development in the heart of booming San Francisco.

The Caltrain yard alone, at Fourth and Townsend streets, covers 20 acres. Add a few more acres down the line where tracks would be removed, and you have what Lee’s office calls “exciting areas for growth and new housing.”

“It certainly would be that,” said Oz Erickson, who has 30 years of experience building housing in San Francisco.

Erickson said the freed-up land would accommodate upward of 10,000 housing units — plus office space and retail, depending on the final plan and zoning.

Estimated value: $1.5 billion or more.

Something to think about.

Demo derby: Tuesday’s special — and special-interest-fueled — election for the state Senate in the the East Bay between Orinda Mayor Steve Glazer and state Assemblywoman Susan Bonilla has turned into a head-on collision between the business and labor sides of the Democratic Party.

And in an interesting twist, Republican voters, who are in the minority, could be the deciders.

“It’s the only show in town, and everyone is paying attention,” said Corey Cook, political science professor at the University of San Francisco.

Labor Democrats backing Bonilla are incensed that Glazer is getting help from independent expenditure committees funded by Republicans outside the district — but the fact is, both sides are courting the GOP vote.

Bonilla, for example, is pushing the endorsement she got from Contra Costa County District Attorney Mark Peterson and other local Republican officeholders.

And with good reason. The latest numbers compiled by the firm Political Data show that Republicans account for a third of the votes that have been mailed in to date — meaning they are not sitting on the sidelines just because the runoff features two Democrats.

Both sides are predicting the a race down to the wire, but a KPIX/Survey USA phone poll of 684 likely voters taken May 12-13 had Glazer with 45 percent of the vote and Bonilla with 35 percent, with 20 percent undecided.

Democrats were backing Bonilla 2 to 1. Glazer, meanwhile, was leading among Republicans 5 to 1 and among independents by 20 points.

Interesting to note that the poll found voters in the district favoring a ban on BART workers’ strikes by a 2-1 ratio. That just happens to be the issue Glazer has been trumpeting for more than a year.

Stamp of approval: Former San Francisco Supervisor Aaron Peskin may be challenging mayoral appointee Julie Christensen for the District Three seat he once held — but he’s not looking for a fight with the man in Room 200.

At the annual Chinese Chamber of Commerce spring banquet at the New Asia Restaurant the other night, Peskin told the crowd that he and Mayor Ed Lee “worked well together in the past, and I look forward to working together in the future.”

Does that mean Peskin will endorse Lee for re-election?

“It’s possible,” Peskin said. “But it’s still a little way from June 9” — the filing deadline for anyone who wants to take on Lee in November.

Sad news: It’s been a gut-wrenching couple of weeks for Oakland City Councilman Larry Reid.

First his 21-year-old nephew, Dawud McGuire, who suffered from asthma and diabetes, fell ill at the Coachella Valley Music and Arts Festival in Southern California and later collapsed. After several days, the Arizona State University student was taken off life support.

Then Reid got news that his 47-year-old brother, Terry Reid, had suffered a heart attack in Cincinnati. Just 12 hours after Reid’s nephew died, his brother — also Dawud’s uncle — was taken off life support.

Upshot: Reid and his wife helped bury his nephew on a Thursday in Southern California, then drove home to the Bay Area and caught a flight to Ohio for the funeral of Reid’s younger brother Tuesday.

“It’s been very hard on the family,” Reid said.

New star: The Rev. Joseph Illo, the controversial conservative priest at Star of the Sea Catholic Church, has been replaced as the parish school’s chaplain.

Illo, who allowed the distribution of handbooks referencing sodomy, masturbation and abortion to students as young as 7, was replaced to “assure an atmosphere of calm,” Archbishop Salvatore Cordileone wrote in a letter to the school principal.

“This change does not indicate any lack of confidence” in Illo, said Cordileone, who has come under fire himself from some parishioners for pushing a traditional, conservative agenda. “For my part, I applaud the many good things that he has done.”

Illo will stay on as the parish priest.

Star of the Sea parent Christy Brooks met with the new chaplain, the Rev. Vito Perrone, and said it was clear “that he sees us all as children of God. That is something we did not feel with Father Illo.”

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or e-mail matierandross@sfchronicle.com. Twitter: @matierandross