Mindstorms Software Versions
You probably don't need it, but the LEGO Education NXT 2.1 Software is still for sale through LEGO Education (at least in the USA). They do not advertise and upgrade price, but it does not hurt to ask.
The Energy Meter blocks are available for download on the LEGO Education website. I went to http://education.lego.com/en-us/downloads and checked the box "Blocks" under "Download Type" and it shows up in the list. It does not say if it is for NXT or EV3 though. Also, I found this for the NXT Temperature sensor.
I would not recommend using the EV3 software for programming the NXTs. There are a number of limitations, such as lack of support for 3rd party sensors and lack of support for Bluetooth. Also, I understand the programs take up much more memory this way.