Longmane,
I would not be all that concerned about banquets and such becoming an everyday routine. There are several reasons that will likely prevent that:
1) The banquets should cost gold, and to gain largesse out of it one would need to keep increasing the amount of gold spent. This gold is away from the war effort and other important gold sinks, so spending excessively during a crisis would be frowned upon.
2) It takes time to travel to the banquets/hunts etc. and it takes time to attend them, which is again time away from the war effort, border patrols, courtier work, preaching etc.
3) If there are parties every other day, people grow tired of them and/or only pick the ones which they think are more important or more fun. Moreover, if there are several taking place at the same time, those willing to attend parties need to make choices there. Some people will have banquets with very few or no visitors, causing a prestige loss for embarrassment. Paying gold for losing a stat will soon lose its glamour.
4) If it were to be made so that increasing the stats with banquets got progressively more difficult, the banquets could not be endlessly milked for stats. On the other hand, if you really succeeded to get prestigious nobility visit you in great number, time after time, and paid for it all, you probably deserve those stat increases anyway.
But on the other hand, if there is a temporary lull in the action, a period of banquets and hunts just might liven the things up a bit. The banquets would anyway be more of a way for encouraging RP and communication that is not always about warfare. They would offer opportunities to be a little more relaxed, which might hive some more flesh around the bones of the character personalities.
You could also add an infiltrator button "poison the wine" with a higher chances of success compared to your standard stabs, you make large parties with many foreigners somewhat more of a risk. With more people around there is always more plausible deniability. Then you could add in a slim chance of accidentally poisoning another random guest. Then attending a banquet could always become more of a risk.
Masquerades would make the job of an infiltrator all that more easier too...
