I do use training hall, when I have cash to throw away. But yes, it’s extremely underwhelming.
Even choice between exp boost options is kind of trivial.
+40% for 2-3 days = total average 100% boost in days*exp. Makes sense on short trips.
+30% for 4-6 days = 150% default pick.
+20% for 6-8 days = 140% BAD option, never use this.