Special wiring, lol. You don't need 'special wiring' you just need to run the proper gauge. There really isn't anything special about it.
As I said to Skier in a pm, you have to figure out the cost to run a conventional water heater then amortize the cost of the tankless one. If you can't recoup the cost over 5 yrs or so, then it really isn't worth it.
I didn't read this thread prior to responding but the leaking is a common issue. It can cause thousands of dollars of damage if you don't catch it in time. 99.9% of homeowners don't drain their tank once a year to remove scale out of the bottom of the tank and this leads to corrosion leaks. You should get 15 - 20 yrs out of a conventional heater but most only last 10. With a tankless you never have to worry about it again.
I have seen installs where they have 1 big main unit but for the most part, they are point of use. In other words, you put various sizes in the rooms where you need hot water.
The point about heating the water while you're asleep and at work etc is one of the main reasons one should go tankless. Even though new water heaters are very well insulated, you lose so much evergy via the pipes. What you do is heat the water and keep it warm. Then you have to run the water to get hot water at the point of use. So you've heated the water in the pipes, then let it cool, then drain it to get hot water, then fill the pipe up with hot water again and let it cool. This adds to your cooling costs in the summer as well because you're basically using electricity to heat the water, then electricity to cool it.
I recently designed a house and designed it so the kitchen and 2 baths were all directly over one another. This means no long runs for hot water. Then I had a small point of use water heater for a powder room at the other end of the house. I also looked into tankless point of use ones but since I ended up finding a dream house pre-existing, I didn't need to go further.
Skier: $1400.00 to re and re a water heater is a rip off. Unless you're going with a 120 gallon replacement or a ferrari water heater that costs $1000.00. I typically charged $700.00 including a 40 gallon GE HE water heater and this included the disposal of the existing unit. It should only take a couple or three hours for one man and a helper. Unless it is in a very difficult spot. I even charged a neighbour only 5 hrs and their's was in an overhead bulkhead and had to be jacked up into place.
Now for installing a tankless one. The expensive part (and damaging) is if you have to run 10/2 wire from the breaker panel to the location(s). There's a LOT of cutting of drywall and routing the wire from the basement. Once in though they are very discrete. If your basement is unfinished even better.