I think there are actually 3 - 5 stages of sensor cleaning:
stage 0: use camera cleaning itself (of little use in my experience), check result
stage 1: use blower a few times at angles, check result
stage 2: use lenspen gently, check result
stage 3: use fluids, check result.
stage 4 : if still full of blodges at f/22 try a professional service.
So : do not forget about stage 2 BEFORE going to stage 3, the very last and most - potentially - destructive one. Good luck!
Fully agree, esp the last comment. Doing stages 0-2 properly and checking the sensor with an illuminated magnifier is tbe best protection against causing damage at stage 3.
My only addition is that I would use a Copperhill brush before the Lenspen at stage 2.
If you do stages 0-2 regularly and change lenses carefully then stage 3 should be needed only rarely. Things tend not to stick to the NEX sensor (AA filter) like they do in a dSLR.
Thanks to both of you for taking the time to respond and for the good input. Yes, the time has come for a wet cleaning. I'll proceed carefully, and will soon have a nice clean sensor again.
Again, thanks to each of you who took the time to reply.