That is my point, after a certain number of modifiers, bonus dice and merit you cannot have bad enough dice to tear it down.
You need something like a total of 30 dice+modifiers. While its possible (Especially if assistance is possible, but I'm not sure if it is.), its pretty hard for a starting PC house.
Its not too hard to make there be a low chance of a bad fortune roll (especially if you start in a high wealth area) but its still there. Also the "+1 to something" result isn't actually all that good. Remember you could
have gotten +1 to whatever you wanted.
Thats also the problem with new additional wealth holdings that pop up on the forum.
You would need new tablkes for house fortune if you do not want gamebreakers.
You aren't limited to one holding of each kind. You can have 5 mines if you have enough wealth. (Or one really rich mine.) As long as the new holdings aren't something totally inane it won't be any worse than a port.
For what it's worth, your PCs must be awfully friendly folks to have so few significant enemies that some aren't willing to spend or even burn destiny to reduce another House's House Fortunes rolls.
Just saying, nothing is guaranteed.
Or you know, turning your banner houses against you, framing you for dishonorable acts, invading your lands (blame it on bandits), wrecking your septs... Really if they Also if your house is in decent shape, and no one is causing you trouble? You should
become more and more prosperous. You dig irrigation canals in your fields, train more artisans, build more market places, acquire new tech (pyromancer powders or glass making), build a nice fishing fleet.
I do think that making the house fortunes of an enemy a little worse probably isn't worth a burnt destiny though. (Plus what would a failed test even be? I assume the lightest failure possible, or just -1 to a house trait.)