I like the Symbel a lot and don't want to see it slip away. I think making it entirely about FEPs boosting will hurt it a bit too much. A lot of the feedback here has been about multiplier stacking. I think you can apply a diminishing returns function to cap it. I'm an EVE Player, so I'm familiar with the Module Bonus Stacking Penalty there:
There's a lot of modules that do the same thing to the same stat, and they apply their bonuses as a multiplier. Consider something that makes your ship 10% faster. (Working with numbers I know, sorry.)
Base speed: 100m/sec.
1 +10% Module: 100 * 1.1 = 110m/sec.
2 +10% Module: 100 * 1.1 * 1.1 = 121m/sec.
3 +10% module: 100 * 1.1^3 = 133m/sec.
4 +10% Module: 100 * 1.1^4 = 146m/sec
5 +10% Module: 100 * 1.1^5 = 161m/sec - Note the basically free full effect of a 6th module you've picked up now.
With stacking penalties, the 2nd module only applies ~87.5% of its effect, the 3rd 75%, the 4th 50%, and the 5th 25%.
So:
1 +10% Module: 100 * 1.1 = 110m/sec.
2 +10% Module: 100 * 1.1 * 1.0875 = 120m/sec.
3 +10% Module: 100 * 1.1 * 1.0875 * 1.075 = 128m/sec
4 +10% Module: 100 * 1.1 * 1.0875 * 1.075 * 1.05 = 135m/sec
5 +10% Module: 100 * 1.1 * 1.0875 * 1.075 * 1.05 * 1.025 = 138m/sec
You do still get a benefit from the 5th module, but you only install it if you've got literally nothing better to do. Most ships stop at fitting the 3rd module. Some pure DPS ships will go for 4 or even 5 damage mods, but that's a very corner case application. When you have multiple different mods with different effects, they get ordered so that the strongest bonus is applied first, without penalty, the 2nd strongest goes second with the least penalty, etc, so that players don't have to try and figure out how to control for weird system behaviors.
Symbel already does something like this, I think, there's some wiki text to the effect that filling your table with either items of the same type (wooden plate), or same category (wood plate + earthenware plate + porcelain plate), or just more symbel (wood plate + tankard + linen tablecloth + stoneware vase) results in lowered or non-linear effect of symbel items.
Experience says it's the last case. I don't duplicate items and I'm as spread out in various categories of items as I can be, but when I put that 30% hunger mod porcelain plate on the table, it doesn't go 30% of the way from where it is to zero, it moves like... 2%.
Apparently a) the effect of high quality symbel is still too strong, b) there's off-table stuff that profoundly impacts the table and isn't subject to the same stacking penalties.
I suggest:
1) Make stacking penalties about categories, re-work FEPs/Hunger benefits of symbel accordingly.
2) Make bonfires and Charisma subject to stacking penalties.
3) Reduce the impact of Charisma and additional friends for bonfires (perhaps softcap the benefit by the CHA of all participants? Make those soldiers grind CHA too, if they want to pull these shenanigans... I haven't used a bonfire since W7.)
Also, if it doesn't already, bonfire feasting should absolutely wreck symbel durability. Anyone who's had to clean up after a party knows why...