Unequivocally good? How about the beauty of a manual crossing gate compared to a modern one with its garish flashing lights and siren? How about the old gent who enjoys saying "Morning" to the crossing keeper? How about just having a human presence and an extra pair of eyes with a higher understanding of the locality?
Well, let’s ignore beauty as that’s entirely subjective. Similarly there might be locals who hate the crossing keeper but I understand how a community may feel they lose a stalwart in these situations.
I'm curious to know about the safety and capacity benefits the removal of these gates will bring?
Well, it’s safer to not need a crossing keeper to walk on the track and the road to open and close gates, be that the risk of road/rail accidents or purely a slip or trip. There’s also the risks involved with commuting and just existing at work.
It’s safer to have barriers which are interlocked with signals, so if one is broken once closed, signals get replaced immediately. Similarly to have an OD system monitoring the crossing for incursions and replacing signals in those cases too. And if either of these systems do operate, or have errors, they are all recorded and monitored to either diagnose or replay incidents.
In terms of capacity, this can vary, but in general manual gates are slower to close and definitely slower to open than barriers. This allows more traffic between trains and a shorter down time. But for trains it can mean an increase in line speed, the potential for multiple trains at once, or just no difference at all, as you suggest.
Why do we not have a far cheaper railway by now?
Each person employed costs a huge amount, that’s not up for debate. The railways staff bill for signallers and crossing keepers is significantly lower than it would be if all these people still existed, but I can’t speak for the overall budgets of the railway. The money is used elsewhere, on improvements, maintenance, other staff, etc etc…