The line doesn't need to be electrified? How ELSE are you going to attract ridership?
IMHO, the LIRR should have cut the line to Glen Street years ago, straightened out that stupid curve there, and put in third rail. Glen Cove riders could just drive the (litterlly) extra 30 seconds, Locust Valley ones could go the extra 3 minuites, and Oyster Bay ones could just go to Syosett, which most do now anyway.
Getting rid of the track beyond Glen Street gets rid of a big, complex, traffic stopping grade crossing, plus a few smaller ones. And it gets rid of the slow, curvy track that inherintly limits the ridership at the far end anyway. There's little reason the rest of the line couldn't be at least somewhat faster, and I doubt there'd be much preventing 80mph south of Roslyn. In any case, the extra punch of electrics would help getting out of Glen Street (and also Greenvale to Roslyn), and get the speeds up between Sea Cliff, Glen Head, and Greenvale, not to mention Roslyn to Albertson.
Right now, the OB line has few advantages - it's not anywhere near frequent enough, it's often slower than driving to Mineola or Port Washington, and it's not offering direct NY Penn service, or even Flatbush Ave service. It's ridership is consistantly in the bottom 1 or 2 of the system, and yet it runs through an area that enjoys some of the highest population density in Nassau, and to top it off, is severly constrained roadwise. The line's potential is nowhere near being tapped, and it's pretty obvious that the existing service just isn't going to attract riders.