Water cooling has always been intriguing to me, but I am still very skeptical about the risk and of course it's pretty expensive. As far as longevity goes, the vinyl tubing certainly doesn't have a long life and you need be careful to select compatible non corrosive parts.
Most people (who know what they're doing) use silicone based tubing. The best 1/2" silicone based tubing costs about $2/foot or less if you can get it on sale, and even a loop like mine only uses about 3 feet. Unlike vinyl tubing it does not discolor or become brittle/crack over time.
Even then there is some amount of corrosion that takes place in the radiators and such even with anti corrosive fluid additives, which need be replaced regularly too. PC water cooling systems are really just as complex as car cooling systems, except with expensive electronics thrown into the mix.
I've seen bad corrosion on systems using the wrong KIND of anti corrosive additive, or when people use an additive which is only designed to be anti-fungal and not anti corrosive. I use "Water-Wetter", which costs about $7 per bottle (and I still have half of it after doing multiple systems), and plain distilled water from the grocery store. I've broken down all my waterblocks and radiator and found no corrosion whatsoever after over 2 years of use. Really, as long as you do the research before hand there is no danger of corrosion.
When it comes right down to it it's a lot of risk, expense, and maintenance just to get superior high performance OCing, and even then if you use it for that purpose it's not any quieter than a good air system with a mild OC, in fact usually louder. At that point there's not much price difference between getting faster parts and just mildly OCing them with air vs lesser parts and doing a HP OC with water, and with the former of course, no risk and high maintenance.
The risk is pretty minimal given the benefits. Just do a 24 hour leak test before actually powering on the system. If the cooling system can run 24+ hours without leaking, its not going to leak. I've carted my machine to many LAN parties and have never had a problem with this, as well as everyone I know who has leak tested the system beforehand.
In terms of it being louder than a quality air cooling system, you must have either listened to a system with crummy pump/fan, or are making that assumption based on faulty information. One of the "loudest" pumps out there commonly used in water cooling systems is the "D5" pump (it goes by many brands including Danger Den, but its the same exact pump). Its no louder than an average 7200 RPM HDD.
In terms of "maintenance", every year or so I have to top off the system with about 1/2 cup of coolant. Really, thats it. Only time I've ever had to break the system down was when I put it in a new system, which was kind of unavoidable. :)
Also keep in mind that a well designed water cooling system only needs two 120mm low RPM fans at MOST (mine actually only uses one). High performance air parts typically use 2 on the CPU, and one on the video card, and the performance doesn't even come close to a properly designed water cooled system.
If they were to make systems with better hoses and sealing methods vs just vinyl tubes stretched over barbs, I might be more inclined to pursue it. I've used vinyl tubing a lot for various applications and I've seen how quickly it can go yellow, get stretched out, and lose it's suppleness.
Again, nobody should use vinyl based tubing for water cooling systems for the very same reasons you mentioned.
As far as the barbs go, just use stainless steel/brass barbs and steel wormgear clamps, and you will not have a problem as long as you leaktest everything beforehand.