How on earth did you manage to run 1600 miles in the same pair of trainers without making them look visibly worn??!? :eek:
The "recommended" thing to do (although most likely recommended by shoe salespeople more than anyone else

) is to replace them after 400-500 miles I think. If your shoes were less drastically over this, I would say keep them a little longer, since they obviously fit really well and you aren't injured. But after 1600 miles?!? Check the soles, and try to remember whether the paper-thin parts weren't about 2 inches thick when you bought them

And try out some new shoes in a sports shop, see if you can notice a difference in the amount of support your feet get.
To be honest, yes, I do think it's time for some shiny new shoes

Since the ones you had obviously did very well, maybe you could try and find the same again?