> Does the ride improve significantly on welded rail, concrete ties,
> freshly tamped and cleaned ballast ??

I think the answer to that is pretty obvious. Of course it does! Freshly tamped track also means that it's aligned well and rides smoothly. (Or at least it should...)

The real question is whether the modern track is better than the old style jointed rails. The answr is that yes, it usually is. However, you can also have traditional style track, bolted joints and wood ties, and have a nice ride. I recall riding the Pioneer up the Gorge back in the 1980's and much of the track was still jointed rail. The ride was very smooth, and in most cases the only way you knew you were on welded rail was that the clickety-clack went away.