NightShift, despite the negatives cited, there is some merit to your idea.
Perhaps instead of a classification, members can earn titles. To minimize the overhead effort on the part of the mods, there can be a bi-monthly nomination by players for individuals that have earned titles such as pro-builder or red-stone engineer... etc.
If the mods agree with the nominations, a title can be appended or proceed their on-line name.
This may motivate constructive activity on the server, offer a source of pride for players that put in the effort and let others know who's the right one to seek for advice.