Seems that Lion is a no-brainer, though unclear if a leap to Mt. Lion is advisable; either way I gotta get it on a CD unless that quest fails, too.
Clearly too, they Must have pondered exact steps to evade nuking my Time machine, during transition [in case of glitches no one can predict.]
Maybe will try Chrome first--machine won't care how 'old' is a Lion disc, can decide that later.
Unless Chrome seamlessly saves bookmarks and auto-passwords, etc. from Safari.. an unlikely sale.
(Guess won't ever discover Why safari decided to spring a leak. I 'Trusted' 'them' and ... they failed here.)

But, long-term I may be screwed..
As you are an EE, I find it quizzical that you'd be disinterested in some scientific factoids:
TEMP: the GPU diode is NOT adequately cooled with an ambient of ~80F -- unless you have smcFanControl installed.
I want to see some numbers re the '12+ too-tiny-cased iMacs. Before planning for a 2 yo. model, sometime.
I am not 'paranoid' (carrying that necessary attitude for Beastware), I am experienced with heat VS MTBF as, presumably are you.
(Similarly, I deem it a 'duty' to note daily/usual error messages sufficiently to.. tell the difference as just might indicate Pwned-ership or other anomaly striking.)
NOTHING is immune to creeps-in-action.

Whether Apple goes the full WalMart-Greed road next: also remains a necessary concern, as I can't throw money at their warez
--as their demographic [and lawful prey] seem eager to do.
And I concur that ANY 'update' via Apple:Beastware::Velveeta™:a decent brie.
[Sure glad I don't need a server, though..]

Your lore always appreciated--it's Vincent Shadow grade ;^>