While I was leveling my gatherers (still leveling FSH lol--she's 57 now), I just did the GC turn ins for them (HQ, of course). I gathered them myself rather than buy off the MB because I could get the exp from gathering in addition to turn-in exp.
I tend to use my botanist more than my miner (I use my weaver and culinarian frequently), but the things I gather either I need, or they're in demand on the market and I can sell them. Ores tend to stay the same price/around the same price during the week, and drop on weekends.
Miner: most of the ores that are really common in crafting (iron, silver, mythril, electrum, cobalt, mythrite, adamantite), native gold and gold ore (HQ gold ingots can sell pretty well on my server), alumen, effervescent water (for natron), volcanic and abalathian rock salts, and folklore (lumythrite and crystallized sap, usually).
Botanist: flax, flax, and more flax, logs (if they or lumber are selling well), flax, cotton bolls, stalks of ramie, flax, various ingredients for CUL, sprigs of dust mill, flax, trillium, apricots, rosemary, and folklore (frost cotton boll and wattle bark are the ones I usually go after). Oh, and flax.
(Seriously though. WVR eats through flax like there's no tomorrow.)