Sundays are certainly a problem.
Monday's tend to be even more so, but in the main cities, you can usually find something open.
I can't respond to this part of your query <<"and that serves eclectic and creative foods of the sort that local professionals would seek out">> if you mean cooking professionals.
However, if you mean well off sophisticated restaurant customers, here are some ideas. They meet your other criteria.
1. -A couple of weeks ago I had a meal at an elegant and first rate Italian restaurant behind the Opera House. The Conti. Sophisticated menu, but not exotic. Superb winelist. Really good service.
2.- For traditional Swiss food of the highest quality, old-fashioned ambience - Kronenhalle, near Bellevue. Swiss business people, well-dressed families.
Impeccable service. I ate there last Winter.
3.- Hotel Rigiblick on Zürichberg-
Stunning views from the terrace. (Oops - Just checked- closed on Sundays)
My friends told me that it had picked up a Michelin star after we were there a couple of years ago.
4.- The Michelin two star places - The Dolder and Mesa are closed Sundays.
5.-The terrace restaurant of the Hotel Storchen by the river:
I'm told that the Russian oligarchs who have places in Switzerland eat there a lot. I can't tell from their website if they are open on Sundays.. Sophisticated menu.
None of those places are cheap.
6.-Restaurant Bindella in the Altstadt-
www.zuerich.com/en/vis it/restaurants/bindell a
Perhaps not in the same league,but very good food and wine, clientele is clearly well-dressed and willing to pay.
7.-I pulled out my 2012 Guide Rouge They have list of restaurants open on Sunday . Attached scan.
Conti and Kronenhalle are on the list.
8.-Here are Michelin data -
www.viamichelin.com/we b/Restaurants?address=Z%C3%BCrich&ad dressId=31MzhhMzEwY05E Y3VNelk1TURJPWNPQzQxTX pnd013PT0=
If you are staying in Züri, ask your hotel's concierge to book for you.