However, I immediately abandoned the idea, as a quick glance over the content of my legitimate email - to and from developers, technical mailing lists, etc., revealed that almost all of my legitimate email also contains seemingly random bits of gibberish and pseudowords.

You can still do it and use such a rule with SpamAssassin or others, while keeping a low score so that it slightly influences the results but not too much. Haven't tried it, but Bayesian filters might score good on that kind of real text with random whole phrases, as tech email usually mixes the two together (most spams I get that use these code letters do it all at once, not interspersed with other normal text). -- Vincent Penquerc'h