Well I have a lot of surface area with all my systems, totaly of roughly 250g, top off due to evap. isn't that much of an issue, hell I don't even have it automated yet I still dip a 5g bucket into a 35g rubbermade full of water and pour it into the sump.
Things I've found that suck though are water changes in general. You definitely will want to go to fewer larger ones since a smaller one will end up taking a lot of work as it is, might as well go larger and reduce the amount of times you need to do it. Although I have seen some nice semi-automatic systems for them though as far as having the exact salt level, etc. But you go through salt that much quicker, I know in the grand scheme of things it's not that much, but if you triple in tank size you go through 3x as much salt, filters on your RO/DI unit get replaced three times as often, its little things like this that add up.
And as mentioned the initially setup costs. If you are lucky and have some good pumps, tunze, vortech, etc then it's not so bad just get more, if you had a closed loop or other water movement method on a smaller tank you'll probably find those pumps are too small for what you need (although a return pump does not need to be beefy). Your top of the line H&S, BK, Whatever skimmer you spent a lot of money for most likely won't be able to handle the new tank either. Lights you usually can reuse, and simply add a few more as well as needed. But in general you'll probably have a lot of good equipment you'll need to sell off and get way less than you paid for it.
Electricity can hurt too, if you're like me, heaters are the big issue due to the location of my tanks (not in the comfy area of my main living area of the house).
and of course the need for more corals.. (but thats why we all upgrade right?! 
). The nice thing about a larger tank is more volume..the more volume the easier it is to keep it stable without to many swings.
