How much would CA carpool stickers add to value of 2015 Plug-in Prius? (also, general valuation?)

Prius friends!

California has these sweet carpool stickers that you can apply for, that allow you to drive in the carpool lane by yourself. California isn't issuing any more of them, and they're good through 2019 at this point. We applied for and put a set on our 2015 plug-in Prius.

We're starting the research to sell the car (we bought it so my husband could have a really crummy long commute made slightly less-crummy), but he's no longer working there, so...we're going to find a better home for the car.

I'm wondering if anyone has experience with how much these carpool stickers would add to the car's resale value?

Also, any thoughts on valuation for a 2015 Plug in Prius, base model, with about 28,000 miles on it?

Thanks!