i brewed more than the usual number of consecutive shots yesterday with my silvia and found that the extraction time and flavor began to fall towards the end? are there any compensations that are usual when you do this? is there a limit to good pulls at any one time with a machine?
i temperature surf (30 sec after light comes on) so i would think machine temperature should not be much of a problem.

The group head on the Silvia is only heated when idle by conduction which keeps the group somewhat cool. As you do multiple shots the head starts to load up more thermally so you will need to go from a low shot temp surf routine to a high shot surf routine.

In your case you would want to cool your incoming brew water temp, so either let the time the light comes on go shorter, or maybe if the group heating is enough you may not need to wait on the light at all. Worse case you may need to flush a bit of hot water out the wand to drop the temp.

I am sure RandyG has some ideas that could help.