Hey Paul,
How critical is the obfuscation of the product version GUID in my code ?
You don't need to obfuscate the GUID.
I am trying to see how much effort I need to put into code changes related only to anti-piracy.
If I were you I wouldn't put in any effort. We cover why in the "What is hardware-locked licensing and why choose LimeLM?" article:
The point of licensing isn't to stop crackers from cracking your software. The point of licensing is to increase your revenue by preventing casual piracy (using serials over and over again). There is real money to be made by stopping casual piracy.
I wish there were a way to stop crackers or even slow them down. Unfortunately that's not possible (if it were we'd be on it like white on rice). The fact that stopping crackers is not possible doesn't stop some shady licensing companies from lying to their customers and selling snake oil.
I can go into this in-depth if you want.
So, the short answer is this: just focus on your customers, don't waste time on crackers. Crackers don't buy and customers don't crack.