Alright, I have made up my mind. Your responses have helped me gauging the trade-offs again - merci, merci, merci. I'm renewing my KMC EPT chain, however I will also obtain a simple and cheap 9-speed chain which I will run in summer. This way, the expensive EPT chain will be a little bit better of an investment. And I will try out squirt, once my current supply of ProLink has run out. If that is underwhelming, I'll give NSF a try.
IGH and belt is a very cool thing, but my frame won't allow the belt drive part. But it'll stay on the radar for any future commuter bikes.