I regularly use my PT92 as a range gun since my wife loves it, so if she is coming along, it comes in the bag. Mine has about 8,000 rounds through it, and I have yet to replace a part. I have a recoil spring on hand for when it needs it, but mine is still plugging along. Since it is range gun only and does not serve any defensive purpose, I will not change the spring until it breaks.
IMO, switching the spring to save the locking block seems unnecessary. The locking block is about $50 if I recall, and with the amount of ammo you need to shoot to damage it, $50 is a drop in the bucket.
I am not a Taurus fan - everyone knows it. I am, however, a Beretta 92 nut. And, since the guns are similar, I'll throw my change in....
On the Beretta 92 - the recoil spring should be changed every 3-5k. The trigger return spring has a suggested change rate of every 5k as well... Just to prevent it going out on ya one day at a bad time.
Changing the recoil spring regularly will help prolong the lifetime of the locking block. Its cheap and easily replaceable. Not changing it puts more stress on the locking block.
Beretta's newest 3rd generation locking block has a 20k round suggested lifetime. Taurus has not redesigned the locking block multiple times as Beretta has - so it's of an older style design. If it were me, I'd change it at 10k rounds.
Once you break a block - IF it doesn't damage the frame, these guns tend to break blocks more easily. So, preventing that from ever happening is a wise move. Also, sometimes the frame cracks when you break a block. If that happened, your gun is gone. Usually it cracks one of the frame rails.
Keep chugging away if you want - but I would at least suggest changing the recoil spring regularly. I changed one of mine at 3750 rounds, as it was much shorter than a new spring.
I use my 92's for defensive purposes. Periodically changing the trigger bar spring and slide stop spring is also a good idea as well.