Whatever you use them for, don't run 'em open loop (to either a hot tub or a pool) or you'll wreck the aluminum.
Stagnation temps can be quite high- design the system with safety in mind or you risk taking a 200F+ glycol shower if a pump should fail to kick on or some obstruction develops, or you underdesigned the heat exchange/storage on the extraction end.
Low temp pre-heat for domestic hot water is pretty easy to hack with surplus panels and you have plenty of panel area to do it. Check out some of the DIY stuff they get into at builditsolar.com. See: http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm You could probably keep staganation temps under control by mounting them more steeply than recommended for max-annual gain, and use PEX heat exchangers in a high mass tank (rather than open loop drainback the way Gary Reysa did his homebuilt) for both the DHW and glycol loop. By running it with low temp high-mass storage, as preheat to your hot water heater you get a HUGE solar fraction, and very high efficiency on the panels. You'll need to read up on how to properly set up purge, charge & pressurize the glycol loop, but there's little rocket science involved.