I am a 55 SOLID afflic spec lock. I have respecced destro, and a combination of the two just to see which was the most fun. Affliction is by far the most entertaining build because you have dark pact and siphon so you barely run out of mana and health. I found with destruction you can deal out massive damage with soulfire and shadowbolt, however, your mana drains like crazy and I found myself constantly having to use bandages and food. With solid afflic, there is litterally NO downtime at all and you never have to use food or bandages. I can take 5 lvl 56 mobs no problem and occasionally 6 when I want to push it to the limits. All-in-all, I'd say stay with afflic if you want to take down a lot of mobs fast while maintaining your mana and health and go destro if you want to do HUGE crits. Or you can go for the third tactic and go part destro. I've never done this before though so I wouldn't be able to give you feedback.
Hopefully that helped :P,
Nik