If you want anything on the Levantine coast, the Mamluk policies described here:
http://www.deremilitari.org/resources/pdfs/fuess.pdf must be prevented.
I think the most important point is really stopping the Mongols from so brutally bruising the psyche of the Muslim world. The Sufi and other mystical movements which formed after these invasions were a reaction to the terrible events which had occurred before. During his time as the leader of all the Ayyubids, Al-Kamil built 37 Madrassahs in Damascus alone, which doubled the amount in the entire country, mainly because He saw Jihad as a holy war against laxity and lack of knowledge as well as a military concept. The Mamluks really didn't have the time to invest in the building of such things, and thus moved to the much more military concept of Jihad. This is very understandable when one understand that not only were the Mamluks essentially a praetorian guard, but they were under constant danger from the Mongols, and later, the Il-khans. The fortress mentality that Baibars and his successors such as Qalawun attempted to produce is therefore fairly understandable in the light of events.
As for the destruction of the coastal ports, it stems from the reformations of the Ayyubid Sultan As-Salih. As-Salih reigned after the death of Al-Kamil in the 1230s and he destroyed the decentralized, quasi-feudal
qatisystem which existed under the earlier Ayyubids. Interested in funneling wealth into Egypt as well as making everything much easier to control, As-Salih set the defining system of governance which his General, and later, successor, Baibars strove to maintain. In the earlier Ayyubid state the state was decentralized, much like medieval Europe, into a massive system of prince and landowners. This made such things as assembling an army extremely difficult. It tells wonders of the manipulative and diplomatic ability of both Saladin and Al-Kamil that they were able to keep a system like that together for such a long time.
Such a system also bred disputes; in the succession crisis following Saladin's death several rulers fought for power. Ultimately, Al-Adil(who would be succeeded by Kamil) and Al-Muazzam, along with another whose name escapes me, won out in this battle for control. They took control of the three main hubs of power: Cairo, Damascus, and Mosul. The land itself was decentralized further into the aforementioned Qati system. While this worked fine in theory during times of prosperity, it would falter and collapse in the face of the Mongol horde. It is also intriguing that this inefficient system was employed in many other areas of the middle east and was not an isolated phenomenon. Ironic that the birthplace of the system would be the first to lose it.
As-Salih essentially centralized power into Egypt and Cairo in particular in the face of rising tensions everywhere. The question of what would happen with the crusaders remained apparent, for the fear that Frederick II may make the mainland his imperial domain and begin war once again on the Ayyubids was always a distinct fear, if not necessarily a true one. In addition, the collapse of the Shah's state in Azerbaijan and western Iran, where he had etched out a living with the remnants of his state apparatus until his defeat by a joint force of Seldjuks and Ayyubids opened the very first incursions by mongols into Ayyubid territory. While not that massive, and unfortunately understated by the Ayyubids, it still had a significant effect on As-Salih's planning as the old way of collecting armies, which often took several months, did not work out in lieu of the mongol lightening raids.
Thus, we come to the question of Baibars. He had learned much from his master, As-salih, and had thus capitalized on the vacuum following his death to murder his son, Turanshah, and create a Mamluk sultanate(Though Baibars faded again into obscurity until his victory at Ain Jalut; then he rises back in as a popular leader and then leads a coup to be the Sultan). He kept the centralized structure of As-salih and after he assumed command began funneling as much wealth as possible from the other areas of the empire to Egypt. His destruction of the ports was a very strategic one; not only would this deter Frank attacks, but it also destroyed competitors for trade, and gave Egypt even more wealth. Antioch was absolutely devastated out of pure spite, for they had not been exactly courteous to the Mamluks when they helped the Mongols take Damascus and then turned the Omayyad Mosque into a church. Cilician Armenia received similar treatment, spared only because other urgent matters were at hand.
This also accounts for the relative poorness of Syria in this period. It became a frontier of the empire and was fortified heavily. Like clockwork the Mongols would come down every spring and raid the border regions. Often the Mamluk armies would pillage their own countryside indiscriminately for supplies. Baibars responded to a desperate situation with a daft and radical solution. Of the fleet, there was the inherently obvious fact that as Turkish slaves, the concept of entirely fleet based nations was entirely alien to them and no sultan after Baibars bothered building a suitable navy. Yet even Baibars simply used this to either transport troops to fight the Kingdom of Cyprus or contend with the merchant states. Rarely did he conduct anti-raiding activity, for that would encourage people to go to the Levant instead of Egypt, and he certainly couldn't have that. It's an amusing irony that after the Ottoman conquest Egypt itself faded out of view for the Ottoman golden age, though the Mamluks clung to their old positions like a kitten to laundry string.