Would it be possible to set up a two-tiered membership ……..

and that's exactly what you would end up with.

How long would it be before those chipping into the pot would be requesting special privileges. After all, he who pays the piper calls the tune.

Even if there were no special privileges, the conspiracy theorists would soon believe that they did exist. There's enough dispute and argument, to the point of paranoia, about roles of the mods. the presence of Guests on Mudcat without introducing a new level of pseudo-class distinction where the wealthy can get round the annoyances that the hoi-polloi have to put up with.

DC