I bought my first investment property in Aberdeen in 2019, and I wish that at that time I was better positioned to buy more. I have continued buying properties there and find it to be a market where you can still find deals that pencil out. The golden rule of real estate is, of course, "location, location, location", and by many metrics, Aberdeen has a reputation as the armpit of Washington. However- I think that this has (had) led to an artifically depressed housing market. When I first started buying, it would be common to drive down any given street and every third house was a teardown. As the real estate investment flurry occurred over the past 5 years, a lot of investors saw the opportunity and poured a lot of outside money into the town. You can now drive down "cute" little streets and see many well cared for houses.
The town that was once neglected is being revitalized. I don't particularly think that the demographics have changed dramatically, but the once severely under market rents and values are slowly being brought up to what they, perhaps, always should have been (which is still at a dramatic discount from all other surrounding areas). We also have the aspect introduced by the pandemic of people being able to work remotely. If their option is to live in Seattle, where there job is, or to live in Aberdeen at a 50+% discount, if they can telecommute Aberdeen becomes an attractive option.
Regarding homeless population, it definitely exists. But, as someone who lives and works in the Seattle area, I can say that it is possibly less of an issue in Aberdeen. The major employers in the area are found online and are stable industries. It is (or was) designated as an "Opportunity Zone" which has potential to bring in outside money. It has a large, underutilized port and railways for future development opportunities, but who knows if that will materialize.
That's my 2 cents, and I'm sure there will be differing opinions presented.