So a basic PPL holder (no IMC rating,etc) can fly VFR in a class D CTZ with 5km visibility, but is unable to accept a special VFR clearance!
True, but a SVFR clearance exempts you from the 1000ft rule (formerly 1500ft) under rule 5, so I guess better viz. might be a good idea (not that it will help you when the engine quits).
Tim