Hey jpw23...in the mid-90's I was interested in the Korg N364 but never got near one to experience it personally (I finally went with the Roland XP-50 because its sequencer had percentage quantitization)...have you got a link to any songs you have done with the N364, I would be interested in hearing it in action...
I've never played the N364 so I can't comment on specific sounds, but I think it is a personal-taste thing anyway...I would say if it sounds lame to you and/or if you've played other synths and felt that the newer keyboards/sounds blow the N364 away then it is time to get something else...does it get the job done for you (are you personally satisfied with what you are hearing) or it it just not measuring up?...for me the sounds on my Roland XP-50 still impress me so I don't feel like it is a hinderence to me being creative (though a decade of inovation has occured since its prime).
N Series is the big brother of the X series. The only difference between the 2 would be the POLY, the N series had 64 and the X series only had 32. Sequencers were easy to use. Lot's of good sounds except piano is weak. The rest can be tweeked to your liking.
I have a N264 and N364 (amongst many other newer and vintage keyboards). To be honest my N's are to this day still the workhorses in my rig (especially the N364). BSR2002 was right, the pianos suck (and brass sounds aren't the best either but not too bad), but the N is an absolutely intense keyboard for pads, symphonic type sounds, basses, percussion, and KRAZY FX. If anyone want's some kick-ass p/c/g files just PM me. I actually have a really good piano created with the best program for the N ever: http://www.soundtower.com/synth/n264_n364.htm
As far as what the N compares to, I'd say Roland XP-80. The N is definitely not outdated yet (Hell I see a lot of bands still touring with their M-Series/X-series). Checkout the band Nightwish. He has used an N364 since it rolled off the assembly line. I've had mine for 6 years, and it never ceases to amaze me the new sounds I can coax out of it. To me the weakness in it is the lack of realtime controls (My Karma spanks the N in this department), and the sequencer is kind of a pain with the whole page flipping setup. Get yourself a small MIDI knob controller unit and a computer and that solves those problems.
Hey...I was checking out the N364 on ebay...some are going for $800 +...it seems to be holding its value very well...(I think you could have gotten a new one for $1100-$1200 about 10 years ago)