As several people have pointed out, the original was just plain too heavy for the track - a common problem with early locomotives anywhere.
There is, in the National Railway Museum, York in the UK, a complete sister of the 'Stourbridge Lion'. 'Agenoria' was built, like the 'Lion', by Foster & Raistrick in 1829. It shows the grasshopper beams and the simple boiler that really were rendered completely obsolete by 'Rocket' of the same year. By 1830, 'Planet' had been built for the Liverpool and Manchester Railway, and all subsequent locos show the layout that Robert Stephenson produced with 'Planet'
You can see 'Agenoria' at:http://www.steamlocomotive.info/vlocomotive.cfm?Display=4045
There are several working replicas of very early locomotives in the UK:
Locomotion, Puffing Billy, Steam Elephant, Rocket, Sans Pareil, the Penydarren loco, and some later ones including the 7 foot gauge 'Firefly' and 'Iron Duke'
By all means, go ahead and build the replica - generations of people have never seen these things in action. At best they have a static exhibit, or a few remaining parts, or at worst only photographs or drawings. To see one in action is the only way to appreciate it.
By the way, the same applies to other machines - paddle steamers, vintage aircraft and old cars.