First off, Warranty Companies are Insurance Companies, and Insurance companies are not in business to lose money. Their income is derived from your premiums, and the more of that they can keep, the better off they are.
That said, an aftermarket warranty CAN be a lifesaver! I've seen it firsthand (I'm a Service Advisor for a GM store)...I've seen them cover items I thought would be a definite no-go, and I've seen them deny claims I thought were sure things! There's no telling, sometimes. Usually they won't cover "wear" items (clutch components, brakes, belts, hoses, etc.), unless it's caused by a covered loss (brake caliper craps out and takes the pads with it...caliper and pads might be covered. -OR- Water pump disintegrates taking out the belt...pump and belt are probably both covered). Having a modified vehicle doesn't work in your favor, especially if they send out an adjuster to look it over.
On the other hand, if you don't have any problems (or covered issues) with the vehicle, the cost of the policy was a waste.
All insurance - extended warranties included - are a crap shoot and a gamble. Obviously, some are better than others. If you need them (trans failure, engine dies) they can be worth their weight in gold. If you don't, then you wasted money on what could have been a really nice set of new tires!
Either way, you've got to decide for yourself. Good luck.