Yes, GHz is more resistant to ignition noise.
Thanks for confirming that.
I am with Sai on this. I would convert a MHz radio to GHz and enjoy both the worlds. The MHz receivers are going to be dirt cheap as 2.4GHz takes over. And more people fly in GHz, the MHz channels are going to be free... Buf if I change my mind to go with GHz, I can always do so anytime with my Assan module.
That is just one way of doing things (assuming one is savvy enough).
The point (of this thread, at least) is that everybody including you and Sai are shifting to 2.4. In other words, why take the risk (of getting locked out by someone else) with a 72Mhz "add-on" ? I am not sure price is enough of a justification for most people with a limited number of models. I think the peace of mind, security and other features of 2.4 are a better trade off.
Cost is something that has already come down for the non-premium brands, and is on the way down for the premium brands.