TL;DR version: quit making inscriptions and be a miner/skinner.

Glyphs:

The market for glyphs has already passed. When 4.0.1 was released, glyphs couldn't be put up for sale fast enough. Now that you memorize them for good now, once a glyph is acquired there is no longer need to continue buying them. Most characters now possess all the glyphs they'll ever use, so there will only continue to be a demand by alts and newbs which is only a small subset of the marketplace as a whole.

Economic analysis:

Three years of rampant mud-flation coupled with absurdly high materials requirements for crafting professions will ensure strong demand for raw materials resulting in prolonged premiums in prices.

Anecdotal evidence on my part suggests that prices immediately after an expansion will diminish only slightly over time as a continuation of the increase in money supply offsets a drop in demand.

Which brings up a rant on my part:

As a tailor on my primary character, one piece of Dreamcloth takes 30 volatiles of any one type... I've almost completed Loremaster of Cataclysm, and I haven't seen 30 volatiles total. Supposedly I will be able to "prospect" emberfire silk when I reach a certain level for additional volatiles, but I'm getting so little cloth that it will be a long time til I even reach that level of Tailoring.

Similarly, my other two high-level characters wear plate armor. To make 425 blacksmithing (redsteel bracers, for example) takes 2 folded obsidium, each requiring 2 obsidium bars, each requiring themselves 2 obsidium ore. That's right, the first crafted item in Cata BS requires 8 ore. LK BS started at 2 ore=2 bars=cobalt bracer.