Two nights in PDX.
I agree with all these recommendations, although there are obviously so many others. But you could do a lot worse than Bijou and K&Z's for breakfast and Davis St. and El Gaucho for dinner. Sounds like a great plan. You'll pass through a couple of sketchy blocks on your way to Davis St. but don't worry, these folks are generally totally harmless. Davis St. is definitely worth the short walk from the Marriot! In fact, on your way there you might stop for a cocktail at Gilt Club.
Lots of options - but if you're looking for downtown close in places...
Breakfast: BIJOU CAFE
Breakfast: Kenny and Zukes
Depending on your trip and your palate - if you want to venture out...there are tons of great places on the East side albeit with a much more casual typical Portland ambiance than El Gaucho.