i dont think they have forgetten anything at all, it just no longer makes as much financial sence to rely on a few traders and pander to their wishes accordingly than it does to run the site in the interests of the thousands of paying members.
I remember carbs and points, but I have neither on my car as there is a better way now.

IMHO traders still have the option of signing up if they wish, and in fact many do, but they no longer have as much control over how the site is run as they used to, and IMHO thats better for the members.

That said its a shame if you feel that PF wont bring you enough business to justify 400 pounds a year, as I view you as one of the good guys and are one of the few people selling secondhand parts that I would recomend to people (and do so quite often in fact) as I would have thought that with so many people on here looking for parts, it should be relatively easy to recover that sort of expenditure.

My opinion (like arseholes we all have one) is that you arent looking at this from a purely current business perspective, you feel that you should be in some way rewarded for supporting the site in the early days, and YOU forget that you WERE rewarded for that support by lots of sale.
Either it makes 400 pounds worth of profit right now to advertise or it doesnt, those are the options and I think you should either do it, or not keep going on about it really.