Well I'm not as much of an expert as others here, but even if Toshiba does place a better offer, by the time markets open tomorrow SNDK will be at least around 50% higher. I doubt Toshiba would offer much more, surely slightly more, but not much more, so then you end up buying shares for a price that may remain at the same you paid for, rise slightly, or drop significantly due to unrelated events.
I don't know, I would never buy a stock AFTER an offer was made. But like I said, that's just me. Maybe others here can give a better advice.