Well, on my server the market for enchanting mats has been steadily crashing since a couple weeks after S4. Almost -50% on LPS for example, GPEs have held up better but still down. Arcane Dust is dirt... I don't look at the Void Crystal market but I can't imagine it's much higher than the 2x LPS price cap.

I predict there will actually be a spike in prices at WotLK release, depending on which enchants are immediately upgraded in WotLK. Once it's closer to release you can simply check the trainer recipes and find out what old enchants people will still want because the new replacement doesn't come until 425+ skill. Furthermore, there will be people pushing to skill off the old materials, particularly those of us who are mainly disenchanters and did not push up to 375 skill yet. (next 1-2 month is time to fix this btw).