i will try to address most your questions: the difference in height you have is from the original worn out front springs sagging & looking at your pics the shocks are definitely leaking, not sweating, they are shot & need to be replaced. most people & even some dealers suggest removing the xreas & using standard shocks. new xreas system is $2000+ as you found... just not worth it. you can convert to factory toyota non xreas shocks, many people pull their stock ones to upgrade & they sell for cheap. or you can get aftermarket like KYB, monroe or bilstein. monroe & kyb are very close to stock ride & are not harsh at all, bilstein are usually intended for off roading & are stiffer than stock. if you dont off road & its a 2WD then i would suggest finding low mile used toyota shocks or KYB. monroe get lots of bad reviews for being too soft & after some miles & time that just gets worse, the kyb are slightly stiffer than stock but still a very nice firm ride & will allow more time/miles before they start to sag or soften up.
you need new coils on the fronts, called coil over shocks, monroes term is quick struts but these 4runners dont use struts. if the rear sits high you dont need new rear coils, just the shocks.
the fittings on the xreas shocks are for hydraulic fluid not air, they transfer the fluid to the needed shocks like on a corner or hard bumps etc, the system works very well when new or in good shape but they are known to leak like yours & are too expensive to replace. its not very hard to remove them, there lots of write ups here or even youtube, if you cant or dont want to work on it, check with some local independent mechanics (not the dealership) you just tear the lines out & it doesnt take much time, probably an hour or 2 labor added to replacing the shocks. also the new shocks come with new hardware & top hat bushings so its an easy install without swapping springs etc.
i removed my xreas on my 4wd & it was very simple, replacing the shocks was easy too aside from one front being a little stubborn to come out of the top hole but a little prying got it right out. after 1.5 years i am very happy with the KYB's, i dont do any real off roading but im sure they would be fine & better than stock if i did do some light duty stuff but they ride great on the road & lifted the front to look much better.
sorry for the long post, hope that answers most your questions. remove the xreas & get either used original toyota shocks, (pretty sure early 5th gen fits 4th gen) or get the KYB's. they are lifetime warranty too if theres ever an issuue.