That's not as bad as it may seem - if I recall correctly, the big yellow capacitor that blew up is a suppression filter. It's meant to protect the computer from power spikes; when it gets old it can blow up with a lot of black smoke as it happened to you, but it's nothing too serious. The Mac could even run without it!

What I would do, if you're practical with soldering, is just starting to replace it - there's a list floating somewhere with the exact replacement component to use, which now I don't remember. When you're at it, you might look around the other capacitors (possibly even remove them) to be sure there's no leakage going on - I can see some traces of corrosion in the second photo, so I'd definitely check their condition.