The Holy Roman Emperor still is a position of prestige, and can be used to build up a stronger support base. It depends a lot on whether and how the player tries to use it, ofcourse. The Reichstag could be used to raise money, and it might be possible to mobilise the Empire against a common threat, though that requires diplomatic finesse.
I'm presently pondering how to model the Eastern Zhou king, who is pretty similar in some regards and less in others. IMHO the fact that the HRE was elective was not necessarily bad for the office, as it could be uplifted by the election of a suitably powerful monarch. Zhou has no such opportunities, and also has an increasingly impotent dynasty in power, though there were attempts to change it.