For mercenaries, I suggested a long time ago that there be two taverns as follows:
1. Low end tavern for cheap mercenaries, they still have their place in the game for smaller guilds who do not need the high level expensive mercs;
2. High end tavern for the high end mercenaries only, say level 400 and above.
I am not fussed if you have to upgrade some structure to allow the above feature and/or I would be happy to pay more to the scouts to increase the likelihood of finding better mercenaries.
I get bored and tired of seeing the same low end mercenaries reappear when i am cycling through the offers, mercenaries appear that would frankly add less to my group stats than one buff would.