Situational Modifiers for Intimidate

A few times in the last few weeks, I have not followed the rules for the intimidate skill as strictly as the rules as written would suggest. Of the social skills in the Pathfinder game, I think it is the worst as far as its execution. Both bluff and diplomacy have modifiers based on the context of the conversation. Telling a far-fetched lie, for example, is much more difficult than telling one that is believable. Intimidate, on the other hand, only factors in hit dice and wisdom modifier (and sometimes size) no matter the circumstances. Personally, I think that's ridiculous. Here's a set of modifiers for the intimidate skill that I'll be using in my campaign...

You and What Army?
When you try to intimidate someone, numbers matter. Allies can make an "aid another" roll to increase the chance of intimidating, so in some groups it isn't that difficult to rack up an extra +6 to +8 just because your buddies are standing around. But what about the target's allies? Shouldn't they similarly be able to bolster their buddy's confidence? Instead of making dozens of rolls, this simple modification to the intimidate rule should represent this effect without having to make any additional dice rolls:

DC = 10 + HD + Wisdom modifier +1 per ally in sight that could help prevent the threat

This makes it much tougher to intimidate the leaders of large groups. Whether it's because they actually don't feel threatened or because they just can't show it in front of their followers, leaders are much less likely to respond well to threats, especially when they are being observed by those who look up to them.

Size Matters
Even though this is already written into the skill, I think it's a little too simplistic. The difference is always plus or minus four regardless of size difference. Apparently, a colossal creature is just as easy for a human to intimidate as a large creature as long as they have the same number of hit dice. We already have a table that represents some numerical differences between size categories. If it applies to attack rolls and armor class, why can't it similarly apply to bluff checks? If the size of the creature using the intimidate skill affects the DC of the check and the size of the target affects the bonus to the roll, we have size-based modifiers that don't require learning a new table.

Yeah, Right
If a paladin threatens to turn you into a toad if you don't obey, you probably shouldn't be too worried about it. If a witch says the same thing, you might want to consider following her directions. How credible the threat seems to the target should play some role in how it responds. Thus, I don't think it's too far fetched to apply the same modifiers for the bluff skill to intimidate DCs. Just take this table and replace the word "lie" with "threat."

Are there other situational modifiers that make sense to add in?