Spend more money on the amp or the pre-amp?

Mostly great suggestions, but I would advise caution shopping for used or vintage equipment unless you are prepared to work on it yourself or pay a technician $85.00 an hour.  At the OP's price point, paying for repairs or upgrades is probably not an option.
Seems strange to say this on Audiogon's forum.  This is actually a great place to buy used equipment, as most sellers are audiophiles themselves and know the value and condition of what they are selling.  You will usually find good, fair deals.  When shopping on the open market, however, caveat emptor.

Spend it on the cables

I bought a Rotel RB-1552 MkII here for $300. It is dented on the top but sonically it is perfect. If you keep your eyes peeled and stay patient you can find great gear. The DC offset on mine is so low it's hard to measure, and it is quality gear. That would leave $500 for a preamp and you have a lot of options at that price point. If we knew more about your source and speakers we could recommend something more specific. Do you prefer tube or SS sound?

If I'm not mistaken group, (leemaze) was using $800 dollars as a nominal figure, a hypothetical to obtain a ratio, not an actual amount for his budget, - eg: 50/50 or 75/25.

Still "leemaze" my experience would have to say .... it depends.

 Are you going analog, or digital? Vinyl IMHO is more pre-amp dependant than digital.

If you have efficient speakers (eg: Klipsch Horns) that are easy to drive, a good clean high current amp is all you need, so your bias can weigh towards spending more on a snob pre-amp to obtain that desired sonic signature.

On the other hand if you are using a low impedance speaker (eg: Martin Logan Monoliths 4‎Ω-2‎Ω), you're going to have to take care when it comes to the amplifier you select, so the ratio will tilt more towards amplifier selection.

 To provide a loose rule of thump for you, if you have an analog set-up that is, or borders on esoteric (separate tonearm & cartridge), my experience would roughly be 55% - 65% of your budget should be towards your pre-amp ( TUBE Pre-amp .... if going that way, tubes should be factored separately).

Hope that helps.

Hi thehorn,

yes, exactly - this was meant to be a more theoretical/academic than applied question. Your insight is interesting and seems to make sense. It is interesting to hear that many folks find an integrated amp to be the best value at those price points. Because I’ve heard elsewhere that "separates are always better".

Concerning my system(s) specifically, I listen to CDs and google play streaming Via airport express airplay.

system 1:
KEF Q Compact speakers
NAD 304 integrated (just got the audioquest interconnects)
Rega Planet CD player

system 2
Wharfdale Diamond 10.7 speakers
Marantz PM6005 integrated
Marantz CD5004

I was thinking about purchasing an amp to pair with the NAD, but I’m not sure I love the NAD - it sounds pretty muddy/bass heavy with the KEFs. Would a higher powered amp clean up this sound?