As a frequent techies-picker above 5.5k the biggest nerf I felt was the fact that you can't stack mines exactly on eachother anymore.
I found that the most efficent way to play techies was to take him to the offlane with a null talisman and tangoes. The high armor and half-decent damage you get with the null tali allows for trading hits with many support heroes at a decent rate.
As of the halved dmg/manacost/cd on land mines, is mostly a nerf to laning-stage techies since you're no longer as big of a threat of just doing the mine -> suicide combo to land easy kills. As well as playing techies + tusk now is way worse than it used to be. However later into the game I would count it as a buff since the 20-mine cap was removed, also a minor thing but the fact that you get a higher amount of traps makes TA less of a counter since her refraction charges get removed faster with less loss of damage from your mine stacks.
The gold for destroying mines was a huge nerf, combined with that they dont blow up if they're destroyed. This makes laying stacks in a lane dangerous as you can suddenly feed the enemy with gold if they find them.
He just got a nerf to his soul ring usage, soul ring takes 150hp and gives 150 mana. Previously he could place 1 mine for 125/150/175/205 mana.
Now the cooldown is at minimium 5 seconds and the duration for soul ring is 10 seconds, so he can place 1(?) mine at max with each soul ring usage, thus wasting mana from the soul ring.
Land mines have 9/8/7/5 seconds cooldown, and last time I checked 9 < 10, so if you're in the correct position to place a mine instantly you can always place two land mines with one soul ring usage. Also the fact that soul ring + arcane boots (dropping arcanes using soul ring and then picking them back up) gives you pretty much infinite mana, it's still as much core on techies as a bottle on IO (wisp).
"No longer block neutral creep camps."
Time to farm jungle with techies?
I've actually tried this, by TPing to t2 mid tower (radiant or dire), to place 8 mines in the closest camp and the rest in the closest medium camp, you can with a little luck with neutral spawns, get almost level 3 as the neutrals spawn at 00:30.