Lost bitcoins lead to a reduced supply and a thinner supply flow against demand usually results in a increase in the price.

Does it really benefit other holders? I would say it is a zero sum game; Firstly,it's a regrettable situation for one to lose access to their bitcoins due to carelessness or ignorance and it presents a risk that could demotivate sum from getting into bitcoin; An average Joe would not want to be entirely responsible for their assets, where one wrong move could result in it getting lost.

Secondly, determining what bitcoin are lost is purely down to speculation, except the holders come out publicly and adding some more couple thousand bitcoins into the lost pool which cannot be determined does not do much for it to be a benefit.