Clearair: thanks for the offer - for some reason, I didn't see your posts. The nozzles are fine and although a couple of the inks were rather out of date, changing them hasn't made any difference.
Rhossydd has made a profile for me, which is a noticeable improvement over the generic Ilford profile. I also sent him a sheet of GFS which he used to make a profile for his own 3800; interestingly, it's virtually indistinguishable from the one he made for me, which I suppose indicates that the people Epson employed to build 3800s might have had some idea what they were doing.
I think my problem is more closely connected with recalibrating my expectations than calibrating the monitor. I'd become used to "adjusting" mentally the screen image to anticipate the print when I was using a Huey Pro to calibrate a cheap Dell monitor. I'd hoped that using an i1 to calibrate a new iMac screen would bypass that step, but I now realise that I was wrong.
since Rhossydd doesn't mention his firm anywhere in his profile here, I didn't either. He has now told me that I can, so I shall: it's ColourProfiles.com