I knew it had to be a classic case of thread drift, but I just had to read this one to find out in what context "buying a lot of gas" was used.

Okay I am still on this kick.
When in the members area selecting to upgrade to Gold I see a note:"Lifetime Access to Free Software Upgrades: For as long as your license is valid, you will be able to download free upgrades of the software."

What does "as long as your license is valid" mean.
If I have a Gold then it will always be valid. Or is it referring to a revoked license due to breaking the software agreement?

Yes, I believe that to be the case, (be a good boy and you'll be ok) which is why I went Gold.

You break the AUP to invalidate your license then it's no longer valid ...

Okay I give up. AUP=???

AUP = Authorized Use Policy; TOS = Terms of Service, etc...

Basically, if you follow the License Agreement you don't have a worry in the world... Link to License Terms

Okay Giz but here there is no such thing as AUP.
There is however a "Terms of Use " Policy.
That is what confused me with your post.
I already know the Terms of Use here

'eh some sites refer to them as authorised use policies, other terms of service, others have both; blah blah blah ...

Can we pay a little every year (say $99) towards a gold license?

No, but you can pay yearly to renew your member area access ...