Twin Rails is good, but parking can be hit and miss as you are parking on a main road. Good space for your bikes in the accomodation though.
Stopped in a great converted miners house last time, but only sleeps four though, has garage with bike repair kit and a Jacuzzi in the garden!
For food, try the wood fired pizza place in the centre of town near the Wetherspoons.
Yes, Merthyr is different from most English towns as is Dunmfries, but just enjoy somewhere that is different and avoid the generic high street brands that litter our nation.