As a trained researcher, features writer and frequent user of the macro and micro (within forum) search functions, what you have done is simply fantastico!! This is a truly fine example of the mating of the gods of intellect and sex (metaphorical, that is)!!
But, you know what is missing? and that might save space and time?
i) some way to condense or abbreviate the index herewithin. Hmmm... perhaps alphabetically (a - c or a-g, h- p or some such) which is easily understood;
ii) a master index - an index of all forum indexes (?) er...indices. Any cross-referencing is of course welcome...perhaps by alphabet and subject sub-categories (think you mentioned this earlier);
iii) standardisation in the form the forum indices take, and these to be reflected in the master index.
Just a few thoughts...
ATP