Promoting a thread to the home page greatly increases the response, as one would expect.
It is not possible to promote a thread if its first post
So e.g. most trip writeups cannot be promoted. The obvious workaround is to make the first post a brief one.
The 600px figure is worth bearing in mind. I have often edited the first post of a particularly valuable thread (of which we have many on EuroGA) to resize a graphic. In most cases it is not noticeable.
Solutions have been looked at but all seem to be very expensive, and mod time consuming to operate.