In response to both of your points...
My own interpretation of the Buddha's words would be to translate the Prakrit root "కామ" (Kāma) not as desire but rather as craving. The words, though can be used as synonyms in a language like English, are fundamentally different.
Desire and ambition are one thing and craving or lust are another. The former is indeed a motivator, the prime and principal motivator of all human actions, for without desire there is indeed no motivation for life (read my earlier point aboit nihilism.) However, cravings tend to be based on urges, and revolve around material planes: the craving for wealth, property, respect, popularity, pleasurable company, power, so on and so forth. It is such cravings that wrought the near-ruin of Dharmic philosophy and brought about the casteism and racism that is prevalent even today in India and in the world. The Buddha realised this, being not merely a sage as people remember, but also a shrewd statesman (it is worth recalling that Gautama was born Siddhartha, a prince of Lumbini and destined to be King himself) who understood the power of unity among people through peace and wisdom, not through war and combative strength. Buddha, in his own fold, ensured the continuance of Dharmic philosophy (minus the frills, but we've already discussed that in my earlier topic about Hindu revivalism.)
One even could say, that the Buddha himself exhibited motivation via desire: his desire to bring about societal transformation, his desire to preach and teach, his desire to do good. It is not logical, therefore, to say that he would disclaim desire and say it was an evil to be discarded by those who seek emancipation. Desire, indeed, should be motivated by a greater and altruistic cause, as opposed to craving, which is always selfish and seeks to enrich the personal at the expense of the social.
I think I've answered the first part of your query. And yes, the idea of Brahmanic or Buddhistic life precludes material pleasure. That ia not to say, that one must not enjoy good food or pleasurable company, but that is a question of personal morals. A man may be an abject glutton or a womaniser, and yet may be a devout spiritualist and may do great good to society (many kings are of this nature; by the circumstances of their life and nature of existence, a king is used to great food and a harem, but that alone does not make him necessarily materialistic at the expense of greater good); as you say, the true spiritualist is motivated by more that just that. Eat to live, not live to eat, in a nutshell...even if you do eat gourmet meals and live like a billionaire playboy, it's a question of whether that's incidental to your larger motivation or of those things are all you live for.Personally, I believe in the old maxim of my family, "Moderation in everything, including in moderation." Life, as the Buddha also agrees, is motivated by desire and rewarded by happiness. We live in order to be happy, and while ideally the best happiness is from fulfilling one's Dharmic duty, it is not to say that happiness derived from a good meal is sinful! The rule of being moderate in one's pleasures only supports this further.
As Chanakya says in the Arthashastra (lit: Treatise of Economic Polity), the greatest socioeconomic political work ever written (beats Machiavelli's The Prince by a long shot, and predates it by several centuries. I strongly advise all people with a desire to lead, or at least a hunger for statecraft knowledge, to read that)... anyway, as Chanakya says:
"A person who consumes moderate meals, has control over his mind, performs his social and personal duties as per his Dharma, and who involves with his wife for offspring (not mere pleasure) is a true Brahman."
Didactic and fairly blunt though it is, the idea of sexual intercourse for a spiritualist is therefore a chaste ritual to be performed solely with one's partner, and solely for begetting offspring. Likewise, eating is merely a necessity for living, no matter what and how you eat, as the case may be depending on your position in life. What Chanakya tries to say is that the Spiritual philosopher treats pleasure as incidental and principal to his motivations. Personally, I'm straitlaced about sex, and I agree with the fact that if it is performed for any other reason or with any other person, one is being materialistic and no longer spiritualistic. That does not imply immorality, however; all that is mundane is not unethical or illegal. Especially in today's world of increasingly lax codes of conduct, for better or worse. Neither does iy imply that any person can really be 100% spiritual without a certain aspect of mundanity being part of the parcel, and without such mundanity being immaterial when compared on a social angle to the spiritual actions performed by such person (see my earlier observation about kings.) It's loosely comparable to a balance sheet: if spirituality constitutes credits, mundanity constitutes debits, and they must tally with each other in every balanced individual. But there can never be no debits, because humans by nature cannot be God (see my earlier point on Dvaita philosophy) and therefore cannot by definition be fully and purely spiritual, unless their souls obtain salvation, in which case they are no longer any defibable entity, let alone human.
So yes, in a nutshell, Desire is essential to identify one's human-ness, and identify it as something beyond mere material cravings, which any beast is subject to. Desire is not the cause of suffering, not unless, as Hugh says, one does not have control over one's desires, and falls prey either to anxiety, lust, idle fantasy or any of the other myriad pitfalls that are no more a pure desire but rather a craving yet again.
I'll await your responses to this before I try more prompts. Of course, if you'd like to promote something else, feel free.