If your eye doctor says your eyes are fine you don't need brighter headlights. Some of the aftermarket units are more for show than for performance. The newer cars have headlights and taillights that look like sculpture, works of art. The aftermarket is geared more for looks than for performance. I bought some really beautiful tailights off of eBay and I am going to buy headlights when I get around to it. I like the new ones for the looks compared to the junkyard ones that would be the calculated choice. They cost twice as much but the difference is still very little. The headlights will be more expensive but it is still cheap compared to even one average car payment.

If you want glass, check the JDM (japanese domestic market).

A quick look at eBay seems to indicate that the Previa is beyond the realm of art.