Soggy grass and mowers in autumn just do not go together...
Forget the mower and buy a stihl blower.
Although expensive, they last forever are comfortable to use (have done weeks of 4 hour stints and with no bad back) and keep you a lot warmer than sitting/pushing a mower in November.
Have tried a combination blower and sucker machine in the past and gave up almost immediately with trying to collect them - you are better off with a rake and wheelbarrow.(financially and time).
I look after a large garden (50acres) with many trees. Yes a mower is useful to a point, but once the leaves start falling thick and fast, the mower just doesn't do a good enough job.
And you are quite right in wondering if the leaves damage the lawn if left too long, yes - it will start to yellow, the covering of leaves will encourage disease and the worms will start to drag them down, and nothing will hoover/collect/blow the away then!
go and get a stihl catalogue now! (and a bank loan)
linette
http://www.applegategardens.co.uk