I think Portland is generally bad for spanging because #1: It's not a huge tourist spot. And #2: It has a high homeless population. I live in Seattle (when I'm living), and I think Seattle has lots of homeless. I was amazed last time I took a trip down to Portland and saw all the homeless there.
Really, you will ALWAYS do better if you're doing something more than spanging. Even if you're just dancing badly and singing way out of key, people look much more kindly on a traveler doing something to earn their money. You remember when you were little and walked door to door offering to mow lawns, and people would pay you WAY more than you were worth because you were willing to work? You can still do that! If you're healthy enough to be traveling, more than likely you're healthy enough to go door to door offering some service. Everybody's heard the story about the guy with the "will work for food" sign who gets offered a job and turns it down because he's not actually willing to work, and that's what a lot of them think of when they see spangers. When you show you're willing to work, rather than just looking for handouts, people will be more willing to open up.
And myself, I always feel better about money earned than money given without having earned it.
When I'm busking, I've had people try to give me money while I'm still setting up, and told them to keep their money because I prefer to feel like I've earned it. I've had people try to give me money when I'm just sitting at a bus stop playing to pass the time and told them to keep it because I'm just playing for myself. Obviously not a luxury you can afford when your wallet and your belly are empty.