a lot of city driving like you do in hot summers may cause more of an issue then hydro locking, hydro locking isn't as easy as others make it out to be. the splash gaurd under your car will be just fine for driving in the rain and slush. the little water that hits the filter will be dried before it even hits the internals.
my cai has been great no problems yet and we get a ton of snow and a fair amount of rain. no problems at all. just don't floor it in the middle of a lake! lol
fswerks has a sweet CAI also you can get there old version (focus sport cool flo) for even cheaper, it uses the same filter as the new one. F2 also offers a CAI haven't heard much on that one though.
you could always do the stealth CAI at first to save some cash.. i'd personally go with the CAI if i had to pick from a sri or an cai.
cleaning the filter on a CAi is a little more work, you gotta get under the car to get it off. sri can be taken off just by popping the hood.