The Minehead branch was like many others in the westcountry; very busy in the holiday season, but not otherwise. The usual local service stock in BR days [which lasted until 1971] was one or two 3-car sets.
The commuter service never happened, partly because of access problems at Taunton through the cider factory siding which, after closure of the line, occupied the only possible space for a separate line from Norton Fitzwarren to Taunton station. Other suggestions include bus union objections.http://www.unseensteam.co.uk/News-spotlight/Minehead-closurehttps://en.wikipedia.org/wiki/West_Somerset_Railway
I also seem to remember a contemporary article in the press about the problems inherent in trying to operate a regular commercial commuter service with volunteers, and the costs of employing paid staff instead, although I am not now sure this was about the WSR. The problems would be the same, however. The current speed limit is 25mph, I think, which is very slow by modern standards, and upgrading would have significant cost implications.