External soundcard for music production..

1) Firewire > USB

2) latency is not really an issue and will be there regardless of whether you have internal or external soundcard.

3) building a new pc isn't going to eliminate the need for a new soundcard.

4) a quality external soundcard is probably your second most important investment in music production (after monitors)

5) a quality external soundcard is a one off purchase.  You may go through several computers, but you'll always have that quality soundcard.

I've had nothing but trouble with mine 

Things like ASIO not working if you open a WDM application before the ASIO app, audio glitches&streams becoming desynched etc.   Their technical support kept fobbing me off telling me to sort my IRQs out, I tried everything they suggested without any success.  I always suspected their drivers were at fault.  I gave up trying to get any more help out of them when I figured out some workarounds to use the device, but it still means I have to jump through hoops to use ASIO

To be fair to it, my USB isn't particularly reliable for any of my other devices either, but the soundcard is certainly the most awkward piece of hardware I have connected to my computer!