So I've got an opportunity to buy a candy cabinet, a 29" astro city for $900, shipped to me and all. I've currently got a 25" WG monitor in a plain wooden cab. Is it really that different playing on one? How do the monitors fare in comparison? I've got all sanwa parts in my wooden cabinet, so controls shouldn't be much different feeling. Please, post your opinions/advice.
Well, you own an arcade already so you know what's up. Candys are the same thing but they're more full-featured (e.g. they tend to have degauss buttons wheras most US cabs don't), have a nicer and more egonomic CP layout, it's easier to change out the parts, the monitors are nicer, they're lighter and easier to move, monitors tend to be rotatable, etc.
I don't know what you mean by "that different," but personally I prefer sitting down. Candys are better. You're playing the same PCBs so it's not a drastically different experience, but the hardware is nicer.
Those early 90's WG monitors are really good. They're almost as good as a nice Nanao

JP monitors tend to have a ton more caps in them, though, so doing a cap kit is a bit more involved. It's also trickier because most Candys open from the front instead of the back.
The parts are a lot more expensive and can be difficult to find. Is your 100 yen sticker worn out? Your control panel has cig burns? Maybe your power supply explodes? You're going to either have to troll Yahoo Japan auctions until your eyes bleed, get lucky, or make due with what you can "figure out" yourself.
One complaint I've heard is that Candys don't have a space for you to "rest" your palm, but I don't do that.
An astro city for $900 is a bit expensive, shipped that price is "ok" but still seems like a bit much to me. I think that Japanese cabs are easily the best cabs there are, so if you're serious about arcade gaming I would definately recommend buying one.