Building rail to alleviate congestion on well-known traffic patterns is a proven technique for consolidating cost and encouraging social behavior. The economics of it make sense and the technology is being used effectively around the world. Working on outdated infrastructure prevents us from taking advantage of the speed, cost effectiveness and better ecological footprint of the newer technology. By providing an option that is better, faster and cheaper than having an individual vehicle, the HSR has a chance of staying relevant.
No, HSR is not better than upgrading old infrastructure, because old infrastructure is already in place, and can be accessed more easily than created entire new rail systems. New infrastructure is more expensive, and takes more planning. The old infrastructure was developed for a reason, and is probably quite good.