There were plenty of lines that would be extremely poor performing if they still existed, so it's a mighty good thing they were eliminated. Of course, a lot of stuff went before the Beeching era.
Take for example the line from New Radnor to Leominster. More details here:
en.m.wikipedia.org
This was once upon a time my old 'local' line, especially if it had not been closed for 29 years before I had been created. It closed way back in 1955 to passengers, 9 years later for freight. It ran through mostly rural terrain, and even now the villages and towns it served are hardly thriving areas of population. It was not the original goal to terminate outside of a village in Radnorshire, but to continue and link up to the railway through the middle of Wales (without checking this was to be in Builth Wells or Llandrindod Wells, I haven't read the article I linked to), which never happened.
Even if it had stayed opened, the subsidy required to operate the line at all would have been huge. It also doesn't really serve places people actually go to, the majority of that part of Herefordshire/Radnorshire go to either Hereford or Llandrindod Wells, Leominster is not exactly the most exciting place to visit nor the most useful. So where today's passengers for the line would come from, I have no idea!
Closure of the line did help the area though, as the Kington bypass took over part of the trackbed. The town would be seriously crippled by today's traffic if the bypass wasn't there, and if I was a betting man I'd put money on that being the case in many places. Kington being the biggest place on the line west of Leominster, you'd think it would have a station ideally located for it wouldn't you? Oh no, not at all, so even if it had stayed open it would have been useless for the majority of the town.
Similar stories apply to the Titley Junction to Presteigne branch, the branch from Titley Junction towards Hay-on-Wye through the villages of Lyonshall and Eardisley as well as other places, and to the line from Hereford to Hay-on-Wye. I'd be here all night talking about those basket cases, but let me quickly summarise it:
Isolated, rural countryside with hamlets and villages does not make for a well-used railway! Some parts of Herefordshire, and in this case I've moved my attention to the area around Holme Lacy, Ballingham and onwards towards Ross-on-Wye, are so Isolated that you have to have either a big vehicle or walk everywhere. On those roads, I'd not fancy taking my chances walking, and even then it's a long way from anywhere with shops or other useful things!
So, really quickly then, would I want to see much of the old railway still in existence? Of course, some of it would be nice to see, but having seen a lot of long-closed railway areas, it is clear to see why they closed!