This, right here.
The event that essentially trades a stability for 20 Republic Tradition has a MTTH of 10 year, and in a Merchant Republic, the election cycle is 4. Thus, if we rely on the MTTH (Which granted, doesn't always occur, but it's just as likely to occur early than it is to occur late), over two election cycles we'll lost 20 RT to re-election, and gain 28, from both the event and base RT gain.
I'm not saying you'll steadily go back to 100 or anything, because the event only triggers under 50 RT. But it's still a reliable enough way of maintaining a 6/6/6 leader. You should only re-elect if your leader is under 40, preferably in his low thirties. In terms of rulers, my 250 year Hansa game had approximately 24 years when I wasn't re-electing, because the leaders I got were too young. For another sixty years, I was re-electing my leaders up to 6/6/6. That's about 126 years of having a 6/6/6 ruler, which has put me ahead of the rest of Europe in terms of both tech and ideas.
As you can see, my Republican Tradition is also in the mid 50s. So the event is fairly reliable - I did, however, have one hiccup where I went down to 28 RT. Then, I was lucky, and the event fired twice in two election cycles.
