I think you're probably right, though the "your combat actions" line doesn't unambiguously rule out tripping since it wouldn't be "you" the caster taking the action, it would be the weapon.
Still, "if it doesn't say you can, then you can't" is a solid enough arguement for me.
I didn't notice the metamagic thing until you pointed it out but you're right, by RAW you can't use any metamagic on that spell. There's no way that's RAI, though.
As I said, it's one interpretation, but I disagree with that line of thinking since it is indeed "your combat actions" and not the weapon's. My guess is they wanted to emphasize its independence from whatever the caster does. Likewise, the line about it not benefiting from feats is probably intended for stuff like Weapon Focus on the basis of the character not directly wielding the weapon, plus the attack and damage is based off set casting stats.
My favorite use for Spiritual Weapon is
Fell Drain since it deals damage more than once and therefore gets quite a bang out of it.
The whole "if it doesn't say you can, you can't" argument is a difficult one to work with at times. The rules don't say my character can belch loudly, but saying he can't is of course silly. My best guess though is that their intent was for SW to simply make normal attacks as a different spin on a damage-dealing spell, and that other spells that were designed for trips and the like are specifically called out as being such.
I'm not entirely sure what deities even have favored weapons that can trip... Okay, scratch that, I found a great list at
http://home.comcast.net/~ftm3/ASMoNM/FavoredWeapons.html and several of them are capable of making trips. It's not exhaustive though since it doesn't have all of the deities from Deities and Demigods, but it's a great start.
