After months of turbulence, Intel Corp. bulls are finally being rewarded for their patience. But the stock’s sudden rebound comes with a worrying side effect: a valuation so high its most recent precedent is from the dot-com era more than two decades ago. Shares of the struggling chipmaker have rallied 28% this month, adding about $24 billion in market value, on reports that the US government is in talks for a potential equity stake, as well as plans for a $2 billion investment from Japan’s Soft...