Wow, you got all that in 300 miles? Mine look just like that in about 10k miles, and I thought that was pretty bad. But, I've pulled them out looking that bad, and the motor was strill runnung great.
Before I got the valve job at 100k miles, mine burned a quart of oil in 250 miles on the highway, but not so much in town (the oil pumped into the head at high speed and flooded the valve stems I presumed).

So, yeah, you probably need the valve seals, but I have a feeling there is more to the problem, based on your recent experience. Those plugs look bad, and they appear to be platinum tip, which may accelerate the problem.
But, if you installed those new plugs, and car runs great for only a few hundred miles, then maybe it's a combo of bad seals, over-rich, and weak ignition.

So, I kinda back to the original hypothesis - throw in a cheap set of std plugs (non-resistor if you can find them), see how it runs immediately. Check the on-off rastio with the meter as we discussed, then see where we go from there. May be also time for new rotor/wires (however, those parts on the 103 seem pretty bulletproof).

That car looks a lot like mine, I have the artic white with grey leather; awesome color.
The best visual thing I did to mine was replace the wheels with 16" 1992 wheels, with the 9 hole pattern. I'm actually on my second set from Tirerack, about $120 apiece, cheaper than repainting the old ones.

DG