No one wanted to live in Maida Vale when I bought my first flat their in the 1980's, it was dirt cheap, squatter s lived next door, and the building owners hadn't done any work on it in years. I still have it and its worth millions.
No one wanted to live in Kilburn in the early 1990s, squatters again as well as a rough reputation, we bought our house in '91 and we've worked at it for ages. Its now ts worth what a 3 story, (4 if you count the cellar) double fronted Victorian property with an acre of garden is worth in Zone 2.
So quite frankly your advice dyslexic is shit, buy, but buy to make a home, not an investment. Go for an area you can afford it will work out.
The foriegn demand makes up 3.3 % of London demand, the rest is the fact that we have a growing population and not enough supply of housing. Despite the fact that we have far more housing now than we did at the last population peak in 1939, the way people live has changed (e.g we no longer get our teeange children to share beds), we have more single people etc. We also have a huge number of people looking to get on to the market, loads of people aged 26 + are gunning to get in and are looking, not many properties last on the market more than a month, in any area.
Walthamstow is ace btw, it has easy fast access to Liverpool St, to the rest of central by the Victoria line, has the Overground link into the North West and East of the city, has busses that run into town too. The village is a nice area, the market is vibrant, there are a range of interesting palces to eat. Go to Eat 17 one Saturday lunchtime and just watch the world go by, you'll see how nice it is.