So the first thing I bought with my tech points, I went for "harvesting". This got my farmers planting crops and was great.

The second thing I got was "spirituality" because I thought it might make their efforts at boulder-pushing" and such more useful but so far I haven't seen any difference at all....

Any suggestions?

Sometimes in Village Sim (VS), several different tech upgrades are needed to complete certain tasks. Be patient!

In the early part of the game, survival of your village is often your biggest worry. My suggestion is to develop a stable village overall, and in the meantime, just see what happens

Right. Just concentrate on keeping your people healthy and prosperous. Once the village is stable, those tech points will just roll in and you can spend them on the non-essentials.