Ranikhet Express - रेगिस्तान में हरियाली

From a technical standpoint, MEMUs and EMUs are exactly the same.As the name indicates, a MEMU is simply an EMU used for mainline traffic. I would not term the points you've mentioned as advantages, but rather, they are just the design requirements for MEMUs.
Both are designed for different purposes.
1) EMU coaches (12 feet wide) are wider than MEMU coaches (10 feet 8 inches wide) and EMUs are designed for handling more passenger traffic than MEMUs.
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EMU's have a larger passenger capacity than MEMUs. A 9-coach EMU rake is designed to handle 3900 passengers, while a 12 coach MEMU is designed to handle 3300 passengers.
3) MEMU's have better seating and features like stairs at doors, because they are designed to be used for relaxed schedules on main line routes. They are not intended to run at high frequency like suburban trains. MEMUs are just like passenger trains, but running with an EMU-style rake instead of a loco hauled rake. They are meant for passengers traveling relatively long distances, or 2-3 hour journeys. They are not designed for suburban crowds. For example, a MEMU running between HWH-KGP, will share the route with mainline trains, and have 2-3 minutes halts at stations.
EMUs (suburban) on the other hand, are designed to operate quickly. For example, suburban trains in Bombay or Calcutta have many services running just minutes apart. So, they cannot have long duration halts. So, in the 30 second-or-so halt, 100's of passengers have to deboard the train, and 100's of passengers have to get into the train. Having stairs and narrow entrances like MEMU's does not allow for such fast loading and unloading of passengers. So, EMUs have wide doors, and the platforms are constructed at a higher level to remove the need for stairs. So passengers can move in and out of the train much quickly. EMU's are not designed for luxury or comfort. Their only purpose is to move a large number of passengers in very short journeys, and have the flexibility to run a large number of trains in short intervals.

EMUs are usually needed in Suburban Areas where the "Standing Population" inside a coach is very important and it is comfortable to stand for long periods without disturbing others, such is their design.
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With MEMUs, the "Standing Population" is not very important and it is not comfortable to stand for long distances, as it is uncomfortable and may block the path of moving passengers and vendors.
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MEMUs in Suburban Sections can be tried out with Super Locals (HWH-BWN-HWH via Main and Chord both) or with other long-distance Locals having less halts.

For suburban trains, I don't think a vestibule is really necessary. It's not a bad thing to have, but not really necessary too.
The average journey in a suburban train would be less than an hour long. For most people, even lesser. So there isn't a real need to let people move around the train through the coaches.
And considering that suburban trains run with huge crowds, it is probably a good idea to not have vestibules. Vestibules are just designed to let people pass over them, not for crowds of people...
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to stand over them. With the kind of crowds we see in our suburban trains, it will be impossible to stop them from trying to crowd around the vestibule area. This will be extremely risky, and most definitely result in a lot of accidents to passengers.