@ Caravel,

have you tried the XL mod?
That mod increases farm income a great deal, reduces trade income to the extent that you can't rely on trade to fill your treasury, especially with it being threatened by the occasional AI sneak attacks, and it also increases trade income in landlocked provinces. It has also removed the existing land bridges.

As far as your suggestion for linking the Mediterranean islands to the mainland with "land bridges", for me it sort of contradicts your first statement of removing the existing land bridges. I'm not trashing your idea or anything and I can see the point you are trying to make, which is scrapping the naval aspect altogether, but it just seems to alter the map in a huge way that is quite unrealistic. After all, Mediterranean islands held out quite long against large powers close to them, as in the case of Rhodes against the Ottomans, Cyprus against the Egyptians etc. Moreover, several crusades did actually take the sea route: Richard the Lionheart sailed from England to Sicily, then from Sicily to Cyprus, which he captured from the Byzantines and finally on to the Holy Land. Louis IX sailed directly to Egypt, or possibly with a stopover in Cyprus, IIRC.

Once again, I'm not dissing your idea, just presenting a couple of thoughts. If you, however, do mod the game in the way you mentioned, please post some screenies and reports to show us how the game runs. Maybe it would actually improve the land wars.