Funny that you suggest a ride similar to Knott's Wipeout for SFMM's Baja Ridge area. The mountain already had an older version Chance Trabant called Circus Wheel.
Bringing back something like that would help the attraction count, but I don't think a single attraction like that could be marketable for the SoCal market. Perhaps a collection of flats?
But then to play devil's advocate... SFGAdv tried that with its "War on Lines" Campaign. Unfortunately ,that didnt work out and most of those rides are now gone. Then there's the issue of staffing. We already know that SFMM seems to have the hardest time amongst all the LA area parks keeping staffing at appropriate levels.
There's gotta be a way they can get something else going that isnt a roller coaster that still pencils out. The economy is looking up a bit. For me it's not a matter of cutting down lines from other rides, but rather just having something else to mix into your day. The return of summer shows, IMO, has helped that somewhat but there's more that can be done.