mining:
lapis_ore: 11 - Should be at least 20, as they are found in lesser quantities and can not be replaced
obsidian: 15 - Needs to be more, 30-40 per block. You can only mine 240 of these per hour if you are mining them constantly with a diamond pick. That's about 3.6k of XP an hour currently, but you are also not getting gold and instead sacrificing diamonds, plus no one mines obsidian constantly, so you get a bit less than that.
redstone_ore: 11 - Same as lapis, except these are found in larger quantities so I'd say 15-17 since they do require an iron pic.
sand: 1 - Because sand is better power mined with torches, I think to give incentive to actually mine sand it should be 2 per block.
sandstone: 5 - Good, but you are also dealing with sand falling around you so a bit more xp would help compensate for the risk and added adversity factors.