This is kind of a judgement call. To me it would be worth it. And depending on the kind of material you intend to edit, for you it may be necessary.
Even with those upgrades, your system will still be around 10 times slower than a fast system. So you decide.
10 times slower? Are you kidding? Benchmark for
9300 is about 3600 while Pentium 7 is 5500. Hardly ten times faster.
What are you talking about? Passmark CPU mark? Sorry to disappoint you, but a lousy i7-920 easily achieves 9450 score and that is only CPU, the rest of the configuration weighs in pretty heavily when editing.
Just look at the results here: PPBM5 Benchmark
You will see a Q9300 system with 8 GB memory and a GTX 260 video card near the bottom of the list nearly 12 times slower than a fast system. That says it all.