I can lend a little insight into this issue. In the 70's when the RR was being started there were some folks in Georgetown who were vehemently opposed to it coming in to town - for what reasons you'd have to ask them. To that end several key pieces of property with the RR grade running over them were purchased to effectively block the RR. Subsequently structures were built on these properties and on the RR grade. In the 80's the owner of the property between Georgetown Lake and the highway proposed to run the RR through town to his property where he would build a terminal with parking, shopping, a hotel, and a tram to the top of Saxon Mountain (which he also owned most of). That idea got shot down too.
A piece of property on the grade below the high bridge wound up being purchased by another opponent of the RR. In addition the Town of Georgetown threatened to charge a "seat tax" on every ticket if the RR entered the city limits. So, the track ends right at the city limit, and thats probably as far as it will ever go unless the situation changes.
As for the Argentine Central, that's an idea that has been advocated by many over the years, but has strong opponents as well who own property that can block any RR aspirations. Another big issue is parking - there's not enough parking for the Loop operation much less the AC - either in Silver Plume or Georgetown (Devils Gate). So again, unless the political and economic climate changes dramatically there's little chance the AC could be rebuilt. But never say never - who would have ever thought the Loop would be rebuilt? A wealthy individual properly placed politically can accomplish amazing things. Who knows what could happen in the future.
Phil
PS - Kevin, backchannel me.