What I said the first time was not using LV Machines or Parts to craft MV machines and similar. You can still use Low Voltage EU on Medium Voltage Machines since the Machines usually not consume the full Voltage anyways.
Also I DO plan on making Machines decraftable (and that 100% exploit free by saving the Crafting Ingredients as NBT), so you can get 50% (or so) of the Parts you used to craft them back. You just need to use those old Parts (Grinding Heads and Sawblades are not tiered and therefor the same in all Tiers of the Machine) to craft the new and Upgraded Machine.
Some Machines will behave slightly different when upgraded to a higher Tier, E-Furnii will get more Efficient (compared to the Overclocking) for example. And other Machines need the higher Tier just to get the proper Voltage for certain Recipes.
I always disliked the concept of just putting a few Circuits and Coolant on a Machine to make it run faster, you can do that to a Computer, but to a Furnace? Isn't that supposed to be hot? And Macerators? Their rotations would vibrate the shit outta you when overclocked instead of heating up, meaning you need a more stable Hull instead of a Coolant. Every Machine needs an individual Upgrade depending on its purpose, and a whole Set of Tiers is the best way to do that.
And the Transformer Upgrades are also not really that good, they were necessary because of the now borked E-net not having any Amperage, but I doubt anyone used them instead of a 32EU * 256/tick Line back then. And now you can always slam a Transformer Block on the Side where the Energy is going into, what is cheaper most of the time anyways. It might not be that Compact but it works perfectly well.
I will add a complete Set of Transformers from ULV up to ZPM Voltage and maybe beyond btw. so you have Cover Compatible Transformers in case you are worried about your Wiring.
Battery Upgrades will be replaced by the Battery Slots, what is an actual improvement since you can then just take the Battery out and replace it with a better one, what is also compatible with all other EU Battery Adding Mods (and also UE Batteries in case I finally fix UE Compatibility).
MJ Upgrades will be removed entirely, because that is just broken and not worth fixing, since BC breaks it all the time.
Steam, Muffler and Lock Upgrades will stay the way they are now.
Overclockers are only used for some Machines, which are not belonging to the Standard Machines (And I am going to make many Machines into Standard Machines).
@above: I plan to make Multiblock Machines, which are more Efficient than the 1 Block variants (That would be the way to get more Efficient), but that is currently too much work for the 1.7 release itself and would cause a ton of delay.