Intimidation is a pretty hard sell, it's a huge point sink unless you have high will, whereas the better synergy bonus on Persuasion makes it usable as long as you take Mercantile. To top it off there seems to be less Intimidation checks and many of them are pointless, e.g. are in parallel to dialogue options without checks that will achieve the same result, or are in parallel to Persuasion/Mercantile checks. Yell can be a decent defensive ability, but it requires a high effective value to get you money's worth, which only Psions can really manage, the other speech skills are fine but I really think Intimidation should scale with the higher of Strength or Will. Sledgehammer (hence Strength) enemies commonly use Intimidation, and furthermore you should be able to intimidate if you're big and strong, pure Psions with 3 Agi, Str, Dex and Per are physically pathetic yet can apparently intimidate people better than a massive dude wielding Balor's Hammer.