Pickaxes and Plowshares...

So, just playing the game on my own, I find that you can switch between Miner and Botanist without any real penalty. Combined with the fact that theres some benefit to cross-classing their skills (wards, primarily), I'm wondering if there's a reason to not try to level these two classes together?

I know some areas are very rocky and some are very wooden, but is it really that hard to move between the two as you level up to keep the classes close enough together? I guess if you were rushing for 50, it's not a good idea, but what about getting high enough to earn the wards?

Just curious as to whether most people do both, just one, or both until they reach a certain skill they can cross class?

And now that I think about it, do gathering and crafting classes get the 'higher level job' bonus, but only if there's a higher hand / land class? In such a case, if I was only going to level the second class up to getting the wards, I might still prefer to do one, then the other, to ensure maximum XP bonus.

This game encourages cross-class training. Both from the skills and from being able to gather a larger variety of materials.
the only real 'benefit' of sticking to one class is that you level it up faster in the sense that you arent distracted by switching around. Even then, there are all sorts of ways to power level through some questionably broken mechanics to save you time.

Leveling one of them is tedious on its own, I know

Leveling mining and botany together is very nice (currently 21 in both).

1 set of gear + mh/oh
Leves available in the same location (Quarrymill)
Access to almost any material you need for DoH - sometimes amazingly convenient (Quarrymill!!!)