Taxes - Hard to say more should be applied, but reality is different.
First - I don't think we should be subsidizing the purchase of EVs and hybrids at all. The reason - At this time, this is just a subsidy for foreign cars. How can we reasonably be subsidizing Honda and Toyota while 50,000 Americans are getting the axe ? Yes, I know GM has its issues, but this a separate matter.
There is no way you can convince someone who has lost their job that their tax money should go to help buy a foreign car. Personally, I think the sales tax on low North American content cars should be triple the rate on High North American content models.
Second - Hybrids are fundamentally gas consumers, but at a slower rate. If someone figures out how to make a car go 1,000 miles on 1 gallon of gas, go for it. I really doubt that anyone will make a pure hybrid that weights 10,000 lbs that gets high mileage.
Third - Plug ins. If they are buying residential rate electricity in CA to commute to work, it is doubtful that they are saving all that much money. It would not take long to hit the $ 0.20 - 25 / kwh rate. At that price, I am not too worried about the small number of EVs on the road having a big dent on tax revenue for roads.
Solar powered - I hate subsidizing others, but if you can make that work, then I actually will subsidize your road tax until it gets to be > 2 % of the total vehicles. Anyone who does this now is probably just some crazy central valley CPF nut anyway (just kidding D)
Biofuel - Not a big issue here in CA. It is not all that easy to get ahold of a diesel car anyway here due to pollution standards, and the amount of biofuel available is going to be pretty limited. I am not sure about this, but it seems unlikely that even 2 % of the gas could be replaced by biofuel here.