Personally I still think prices have a long way to go yet, Star Wars is a juggernaut and I think there will be enough new collectors getting into it even in 20 or 30 years. In that much time from now the amount of high grade toys and near mint examples will become much less common compared to today I think, toys degrade, get worn, broken, lost, stored away in lofts and forgotten about, etc etc, no matter how much things are looked after the amount of near mint figures will gradually diminish over time.
There might be less of a number of collectors overall in 30 or 40 years compared to today but they will all be collecting from a supply of mint examples that has dwindled, so even if common and lower grade figures drop in value in the future then high grade and rare figures will hold good value. And then think about what vintage Star Wars toys has done to people's perspectives, a lot of people only have to hear the words Star Wars and they see $$$ even with modern stuff, this mentality will be passed on for a long time I reckon and will keep vintage prices on a high for ages.
Just a theory of course!