fighters and other high BAB characters can do this, and for the most part, casters can't.
I am fairly certain that casters can aim ranged touch spells (such as disintegrate, not that I have a reason to) at items to sunder them. Or simply grease them.
Trip - Not every opponent is a Large magical beast with 20 HD. NPC wizards are unlikely to win against a trip attempt, for instance. Facing a squad of drow monks? Ready an action to trip them when they try to tumble past you. And against a CR 10 giant? Having a fifty-fifty chance of tripping such an obviously unsuitable target for tripping is pretty darned good.
I would say that most of the foes actually worth tripping are (not that they are magical beasts, but that the odds tend to be stacked in their favour). In a pinch, they can still full-attack while prone (at a penalty). But tripping is great for preventing them from getting to the wizard. When it succeeds.

Spellcasters shouldn't really care if they have been tripped, since they can still cast spells (defensively) at no penalty while prone. It is a mixed bag - the fighter gets a to-hit bonus against him, but ranged attacks take a penalty.
50/50 against the giant would seem good, but it still seems a tad low to me considering all the resources I have sunk into boosting my trip check. This means that if you don't go enlarge person or improved trip, success becomes even more unlikely.
I admit to rarely ever using classed npcs in my campaign (exception being monsters with a few class lvs), so you have me there on the drow monk squad. Though I would likely just use swordsages and shadow blink to the other side.

Often asserted, never proven. In my mind, specialized = vulnerable. PCs rarely get to pick all their battles, nor is it possible to plan for every contingency.
Issue is, if you don't specialize, I don't think it is likely your fighter will get anywhere, or be any good at his chosen fields as he has spread himself too thin. Tripping is more than just taking expertise and improved trip (else, you will probably fail against most of the foes you encounter). Assuming your DM does not go out of his way to skew encounters against you, I think it might be better to just rock in 80% of those fights, and be resigned to being sup-par in 20% of the rest (or hoping that buffs can help mitigate it somewhat).
