Motordyne Iso-thermal vs Regular Plenum spacer
 

I am contemplating whether it is really necessary to purchase an Iso-Thermal plenum spacer, instead of just a regular 5/16" plenum spacer. The only advantage I see of the Iso-Thermal is not having to worry about throttle body freezing in cold weather. Is this really something to be concerned about with just a regular plenum spacer? I live in Louisiana, and wouldn't say we have extreme cold weather. However, I don't drive my car but a couple days a week, at most, so is throttle body freezing something, I should concern myself with? Any help would be appreciated. I just don't want to do any harm to my vehicle that can be spared for $30.00 more!

Sounds like you might be a bit confused. The ISO Thermal unit includes a manual coolant control valve (ccv) that's used to stop the throttle body from being heated by radiator fluid. In warm climates this extra heat to the TB tends to marginally decrease HP. I don't think you need to worry too much about TB freezing based upon your description..
You also certainly don't need this but I think the real benefit is actually the gasket that goes between the lower collector and the engine block. I found this really helps to reduces heat treansfer up and into the plenum. It's a bit more work to install but nothing all that difficult.

See the MD FAQ:

How important is it to install the ccv. i live in an area where it doesn't get that cold. should i install it and leave it closed?

Its not necessary to install the CCV but it is better if you do. Iso Thermal does not make HP but it does prevent the loss of it. Its good for about 1-2 HP by preventing excessive plenum heat soak as your engine becomes hot. And yes, you will generally leave the CCV closed. Iso Thermal or Copper Iso Thermal is beneficial no matter how hot or cold it gets in your area. Cooler, denser air...produces more power.