I used to work in Canary Wharf before the ELL closed and I have to say changing in Canada Water wasn't a nice experience. Most days I had to let pass 3/4 trains before being able to squeeze in and in a few occasion I had to go back to London Bridge on the Jubilee line.

I think the main asset for Forest Hill is the connections to London Bridge and Charing Cross and those are not going to change with the ELLX, in fact they have got worse.

Sorry all this pessimistic rant to say that if the prices are going up in Forest Hill I think it is because the area in general is getting nicer (new cafes, new gym, etc.) and not because the ELLX.

Also what is the obsession with house prices? If my flat goes up in value I might think "great now I can buy a house", just to discover one second later that also houses have gone up in price. I think it's better prices stay low so first time buyers have a chance!