Thanks for all your feedback.

Generally, is the chance better at Hongqiao or at Shanghai Station to buy a "last minute" train ticket, ie from which station are the trains usually more full towards Nanjing? It seems I'll be a bit quicker to Shanghai Station, either by Bus, Metro or Taxi, so this will probably be my choice, but I've the feeling this station also will see more crowded trains (due to it's more central location) - also in Nanjing, the older station seems to be the better choice to arrive (Saving me about 15min to Xinjiekou) and as it's serviced (almost) only from Shanghai Station, it seems logical to go there, and not Hongqiao.

Still hoping for the 1st April to see a price drop on the early MU service NKG-PVG.. some days they're selling it as low as 100-200 RMB, but currently it's at 880 RMB which will obviously see me taking the train (at least for the return I can just buy my ticket when I get to Nanjing there at the station)