At present this is a bad idea. Simply look at the nature of the creatures forming the California legislature.
Even the Socialists in the Cali Legislature would appoint somebody to protect California Socialists (and Californians in general). It doesn't change the basic dynamic.
Also, If the legislature had the power to appoint senators, it would garner FAR MORE attention during elections. Most people don't know who their state reps are (I guess most people don't know who their congressman is either, but that's besides the point). The hundreds of millions of dollars that get poured into senate campaigns would be redirected towards legislature races, giving candidates greater exposure to the voter.