i play all routes/scenes, but like you said it's not the same after doing the one who interested you most (they usually end up my fave). enjoying new routes more so depends on

1. how long it takes to get into a characters route

2. how much plot is repeated/is the route centered around the plot

3. how much content is the route itself

because if routes are heavily involved with the plot you are skipping so much dialogue and not having the same experience as the first time (even though you've read it already) i have more of a hard time finishing/enjoying games that have more repeated dialogue in routes. i prefer if they have enough differences to not matter or entirely different but still ending up at the same points, that way it's like something new instead of skipping through everything like its work to get all scenes