Actually, you know what, I'm not sure that I have ever suggested a system using a particular gauge soley because a system that ran 50 years ago or more ago in the same city...
Yes you did.
Prove that I was using it as a sole basis. I did not, let's consider Glasgow, it was the last city in the British Isles to abandon trams, in 1962. Now they were built to a gauge slightly narrower than standard and because it differed by less than a width of the rail, dual gauge track would not have been feasible, so a Stuttgarter style gauge conversion programme would not have been possible. It is therefore almost certain that the Glasgow system would have remained at that gauge to this day. However it only differed slightly from standard gauge and no longer exists elswhere, so if I were the decision maker I would choose standard gauge for any new system in Glasgow.
Gauge should be chosen for reasons other than historical methods of operation. If some Turkish city wants to use metre gauge, fine, as I said, it's hardly an odd ball gauge, it's a very common gauge, with lots of equipment available.
Would it be more correct not to base choice of gauge soley on historical methods of operation, why should they not be cosidered at all? The Pennsylvania trolley gauge would become a common gauge if Cicinnati, Columbus and Baltimore were to reintroduce it, then it would be a more common gauge, an idea with which I don't disagree. If you want to know of an example of a new build system, albeit heavy metro, that is built to an "oddball" gauge, check out the BART. For an example of a new build tram proposal where the prefered specifications are based on the previous system in the same city, check out Trams for Bath, see I'm not the only one with this kind of thinking.
Regarding Chemnitz, though translating the German wiki page it seems that they had a gauge of 915mm and slowly converted it to standard gauge because the East Germans couldn't find motors small enough to fit in the truck frames (this seems a little odd to me, given the amount of metre gauge tram systems around, but maybe they felt if they were going to re-gauge they may as well move to standard).
Well, now consider Sophia, they were originally built entirely to an unusual gauge slightly wider than a metre. In 1987 (I think), they began converting to standard gauge, but after the second standard gauge line was complete, they stopped.
For some exmaples of oddball gauge tramways in Europe, consider Braunschweig (1100 metre), Lisbon and Linz (both 900mm), note their trams are quite narrow. It wolud be interresting to see how much extra they have to pay for their rolling stock becaue of that gauge. Neither of those gauges differ enough from metre gauge as to allow for dual gauge track (unless it's interlaced). They could convert to standard gauge and it would be interresting to see if they simply see no point in changing or they intrinsically prefer something narrower than standard.
For an analogy, that nearly all newcomers to LRT are reluctant to consider unidirectional running may lead one to suppose this is because turnaround facilities more to the cost of the infrastructure than extra cabs and door add to the cost of rolling stock and that operators of exsiting unidirecitonal systems simply see no point in changing because the turnaround facilities are already there, yet the European operators Tonyp has contacted say they do intrinsically prefer unidirecitonal running.