I certainly believe there are links between poverty and terrorism, but particularly in terms of the West's so-called Global War on Terror, I believe more important are other variables such as the ones mentioned in the prompt, e.g. perceived humiliation, grievances w/ U.S. foreign policy, radical ideology etc.

For instance, certain of the key 9/11 hijackers were reasonably middle (or lower-middle class) young adults residing in European cities. And while others on this E-mail chain far more knowledgeable than me might correct me, the 15 or so Saudi hijackers (of the 19 total) I don't recall having had hugely impoverished backgrounds, though certainly they were not enjoying the fruits of the petro-dollar gusher as are their local elites.
Still, I'd think, these terrorists were not the hugely impoverished peasants inhabiting the border-lands of South Waziristan and Afghanistan, say. (Incidentally, to mount "A Team" style sophisticated attacks in the West, almost as a tactical 'gating-item', once must enjoy a modicum of education and 'Westerness' to evade heightened security measures, pointing to those most dangerous potential terrorists not necessarily being those mired in the worst of endemic 3rd world poverty).

Meantime, and putting aside the famous example of Mohammed Atta and Co., one might query too whether the Madrid train bombers (mostly young Moroccans) or the July 7th London attackers (mostly home-grown and by the accounts I'm familiar with not desperately poor either), were primarily driven to action by poverty. I suspect not, but for avoidance of doubt, please note this is not to argue a key part of our overall anti-terror strategy mustn't include economic development initiatives in critical areas like the Maghreb, Pakistan, etc, as doubtless poverty alleviation (not least given the demographic boom through MENA and South Asia of younger citizens) will become an increasingly critical challenge for policy-makers in the coming years/decades. I view poverty therefore as a tremendously unhelpful variable in all of this, but not necessarily a primary cause.

Indeed, I'd argue in this Internet and global cable age where IDF airstrikes in, say, southern Lebanon inflame televised opinion in the Islamic World from Tangier to Jakarta, it is more foreign policy actions of various powers, particularly those stoking feelings of humiliation, that create the impetus for (mostly) young Muslim males to join the jihadi cause. This said, local autocracies frustrating freedom of expression are a major part of this toxic brew as well, of course.

Related, I believe there is a 'hard-core' of ideological true-believers for whom radical ideology--and radical ideology alone--provide the requisite motivational impulse towards terror (say restoration of the much discussed caliphate). But I believe there are a good number of 'fence-sitters', some perhaps even tempted towards the faux romance of terrorism by boredom and feelings of alienation while residing in the West, who end up pursuing violent tactics not as much because of ideology per se necessarily, but 'hot topics' like the foreign policy of the U.S., which in turn lead to occasional feelings of perceived humiliation, leading them towards acts of terrorist horror.

Last, I would say the most underestimated cause (per the question prompt) is very likely the occupation of Islamic lands by foreign powers. This has historically been a major cause of Palestinian terrorism (see, over the years, the PLO, Hamas, Islamic Jihad, PFLP, DFLP etc), and see too Chechnya, Lebanon (Hezbollah notably), and more. This being said, the transnational al-Qaeda variety of terrorism has sought to conflate festering conflicts/occupation/humiliation--and then somewhat fuse same w/ 'purist' ideology--so as to thereby be immunized some to the ebbs and flows of localized disputes, the better so there appear to perennially be 'near' and 'far' enemies, the scope of the jihadist playing field is global, and progress in the Middle East peace process, say (were we ever to see any again), would not be a reason to lay down arms.