I think the reason exp has been disabled from the nether is because quartz gives you a lot of exp. You can get several levels in a matter of minutes, and it would be too overpowered.
I use to silk in Nether and then fortune in Mining, and I guess anybody with Nether access already has a silk and a fortune pick. So, to answer you both: you don't really need xp in Nether, and adding xp to Nether wouldn't really cause issues with the xp market. The only circumstance where I "miss" xp drop in Nether is when I destroy blaze spawners, but that's basically scraps. I can't see why not, so +1; however there might be another reason why it was disabled, so I reserve the right to change my mind. <captain="obvious">p.s: xp is not actually disabled in Nether, only xp dropping from blocks: you still get xp when you kill mobs; however I (safely?) assumed we were all talking about that.</captain>
With the current setup you're forced to decide, do you want to spend twice as long to get exp or simply get more quartz. If you thought it was worth your time to take quartz out of the nether for the exp, then effectively doubling that exp gain would be quite dramatic on the market (which is already on a downturn, I might add)
There's truth in what you said, however I don't think the effect is as big as you describe it. I fortune 6-7 stacks per time using super-breaker (which is basically as fast as eff7) and during the time it takes for the effect to cooldown I fill a new 16x3x9 volume batch with ore blocks. On top of that, I'm already used to silk ores even in Mining, I'm not using an auto-switch macro because it would fill my inventory quite fast and I'd have to unpredictably /condense once in a while. And there's some people who don't even have macromod installed in the first place. On the other hand, I acknowledge that many may not have my mcmmo stats/features, so probably the difference would not be as negligible as I previously said (but still less than an average x2 factor, imo).
