Caernarfon station site has been built on and the trackbed elsewhere has been submerged under road improvements. Reinstatement would be horrendously costly.
In Caernarfon, a simple single track standard gauge terminal like that proposed for Portishead need not take a huge tract of land, and it could be built on the grassy bank between the council and Morrisons car parks with little impact on total numbers of spaces. It might be possible to squeeze the standard gauge line behind the Morrisons service station with some small modfications to the canopy rather than a complete demolition.
A corresponding WHR extension along Crown Street could have a terminal occupying part of the car park the other side of Balaclava Road, so no new level crossings would be required at all in the town centre. The two stations could be linked by a new pedestrian crossing over the road. The Crown Street route along the old railway alignment hast safeguarded the route from ad hoc property development which would be much more difficult to remove than a quiet local road which itself has no property accesses onto it. The formation is wide enough to accomodate a low speed narrow gauge track alongside a pedestrian / cycle path.
Even a 30 minute interval service along a branch from Bangor could be attractive due to speed potential and most importantly reliability of journey time at busy times. I agree there are some major and expensive obstacles to overcome on the remainder of a reinstated route, particularly getting through Y Felinheli, but a new station could be incorporated there as well as at Parc Menai that could act as a parkway railhead and serve the local employment opportunities around there. A service on the branch could extend beyond Bangor picking up the local calls further along the coast, more useful for more people than those trains crossing over the Menai to Anglesey. The A55 crossing, although expensive, should be possible as the road is in a cutting, so an overbridge could be built with little disruption. Expensive I'm sure, but no rerouting of a major road for construction as in Edinburgh for the Borders Railway. If there was a passing loop at Parc Menai and every train stopped there at a staggered platform arrangement, a low speed locally monitored crossing (ABCL) over the estate access road might be practical and safe.
A branch could be signalled with modular low cost colour lights and axle counters like Borders and Exeter - Salsibury. The big opportunity would be to combine the work with North Wales coast resignalling when the reconfigured track layouts etc can all be carried out together to save money and disruption. The line is currently controlled by a series of local steam age signalboxes that will need replacing eventually. I guess control could go to Cardiff ROC, but whilst that panders to political considerations, operationally it would be much more sensible to put the whole route including the new branch in whichever ROC will manage the North West of England including the Chester area.
If money is to be spent on any rail reopenings at all, then a short branch from Bangor to Caernarfon would probably be many times the BCR of a long straggling route through rural Carmarthenshire and Caredigion.
