I'd definitely have a board up. We've sold several properties in very different types of location over the years and always had a board. The only time I regretted it was when some idiot set fire to the board! (Naice street with a mix of large 4 bed victorian terraced and a few - also victorian, of which ours was one - detached). Think it was just a random stroke of bad luck as opposed to anything more sinister. We did have a bus stop outside our front garden, so kids tended to congregate.
Even nowadays when most property searches take place online, I think there's still a chance prospective purchasers might be passing and see the board. Additionally, someone who's seen the ad on the portals, but does a drive by to check out the property - if the street is full of identical houses it would help to have a board indicating which one's for sale imho.
I guess not everyone thinks boards are a good idea, as currently in our road there are four houses for sale, none of which have them. These are wildly different properties, from a '90s townhouse to a large Georgian cottage, ranging in price from around 260k to 650k,
Thinking about it, maybe it's because we're a conservation area and boards aren't allowed/frowned upon - when we bought here last year our house did have one, but it was inside, in a downstairs window....