Omrit - Sorry if this is too late, I didn't see the tread until now. I owned the 304 for about 10-12 years until giving it to my brother after Christmas. I listened to it on a daily basis until I replaced it with a 320BEE in February of '05. I think it's a very good amp. It didn't receive too much attention for some odd reason. I think it was only made for about 2 years or so, right around the time when everyone started forgetting about 2 channel gear and started buying A/V gear.
The down sides of the integrated are that it doesn't have a remote, and it is somewhat lower powered.
It's rated at 35 watts per channel. Keep in mind that these are real watts and not Sony Kenwood etc watts. My roommate in college had a 100 wpc Kenwood receiver and my 304 ran circles around it. Their is no real shortage of power unless you are using very inefficient speakers (low sensitivity or effeciency rating). It also has no problems driving low impedence speakers.
It also has a good phono section if you're looking to connect a turntable or thinking about it in the future.
I never had any mechanical problems with mine. It worked perfectly from the day I bought it until today. I drove it pretty hard at times in college and it never once gave me a problem. It was a little difficult for me to part with it.
I have no idea what a fair price would be for it. In the last few years I've only seen about 4 or 5 that were being sold on E-Bay and didn't follow up on how much they went for. One or two of them were cosmetically damaged but reported to be in good working order.
Knowing the amp, and the condition mine is in, I'd have no problem paying $170 for it for someone was selling mine to me (if that makes sense). Mine is in near mint condition. It doesn't have any scratches, missing letters, and works as good as the day I bought it. I don't know anything about the one you are looking into. You also have to keep in mind that the amp is at least 10 years old. Things could work fine today, but you could have problems next week. Or it may give you another 10 years without a single problem at all. Their really is no way to tell unless you know how to fix stuff like this.
A couple of questions - Have you heard any other NAD products before? What speakers will you be using? How big is the room it'll go in?