It was my first trip to Matheran from Mumbai, and I would like to advice people not to book express/ long distance train tickets if you are travelling for a short distance. I went to Matheran in Deccan Express (booked) and found ample of space to seat for our family. But while returning, I booked Sahyadri Express which did not give a pleasant experience, as all unreserved passengers were travelling in the same compartment as ours. Instead a general compartment would have been much peaceful than a reserved one. Toilets were clean in both the trains, but a lot of disappointment with regards to the unreserved passengers sitting in reserved coach and arguing when telling them to get up. Sahyadri Express was 15 mins late on Neral Station and reached about half an hour late at the destination station.
Those intending to visit Matheran, please do not book tickets in advance, as it is very easy to climb a local train than an express train.
Good Luck all !