Yeah, the HRE is an old problem of CKII that Paradox never really tackled. DLCs are good (at least some are), but fixing the game before releasing DLCs would be better. There should simply be a rule, that caps elective titles to rise above low or medium authority or the authority should drop with every new ruler is elected or something. The two big elective realms in Europe (HRE and Poland) both suffered from the fact, that the candidates always had to buy their new crown either literally or by giving the electors new privileges and rights. This weakened them in the long run.
Elective with absolute crown authority is basically a paradox (pun somewhat intended), because the people, that have the right to elect someone, won't be controlled completely by the person, they elect. They might lose the right to elect and than get under some form of absolute control, but both at the same time is nonsense.
An other point is, that it is far to easy for the old ruler to get the heir he wants. My last game now stands around 1370 or so and the Salians never lost the crown. The Emperor of the moment doesn't even have a son (they all died under suspicious circumstances and now some far relative of the Emperor is the new heir.
The overall game would also profit greatly from a weakened HRE, because the HRE makes central Europe rather static, since it gobbles up most of it and never lets go of any land.