its never a bad idea to replace old ignition parts of course but IME if the sparks are weak this is most likely to manifest itself when the engine is warmer and the plugs are trying to fire a leaner mixture at part throttle, i.e. at higher cylinder pressures, not when trying to fire a richer mixture at low engine speeds. The spark jumps the gap with more difficulty whenever the mixture is leaner and the cylinder pressure is high.
This makes me think that the fuelling is more likely to be the problem. Firing promptly every time from cold signifies that you have a functioning cold start valve, but bad running immediately afterwards signifies that there is something wrong with the fuelling thereafter, probably the control pressure but it could be other things such as a slight leak in the flexible fuel pipes from the fuel pump near the engine.
If there is a tiny leak then not only does fuel bleed out (which can make a strong petrol smell on a warm engine, NB you will only see wet petrol on a cold one) but air bleeds into the fuel line when the engine is stopped; this means that there is a mixture of air and fuel in the fuel line when the engine is started from cold. This is rarely so bad that the engine won't fire when the cold start valve opens, but (with most fuel injection systems of this vintage) it can interfere with the fuelling from the main injectors until the air is cleared from the fuel system.
cheers
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