If you "swap out" the faulty electronics, you may also replace this firware data (fleshed to an EPROM) too. You just ensured that the original files could never be recovered!
The filesystem, if I understand correctly, stores information about where disks' files are located. Thus, true, you would not know that sector xxx2 was bad, but you WOULD
know that there is currently NOTHING
stored there and
that your file is located at sector xxx3 and
be able to read it. If
you were to resume use of the drive, true, you would need to do a full format (not quick format) or use another drive software, to map the bad sectors out into the filesystem to recreate what the firmware already had. Or you could use the drive manufacturer's tools and do a manufacturer recertification scan. I know for a fact Maxtor releases these tools and I do believe every other drive manufacturer does too.
... I also recommend NOT to use any of this with CRITICAL DATA.
What you are saying is correct about not doing any of these practices with valuable data. If your company can afford $2,000 a pop to do it, by all means, use the professionals and don't get stuck trying any of this. I meant this post for home users who lost their models, documents, programming source code, etc. and can't afford $2K to fix it. It's much better than throwing it in the trash and... -bonus-! half the time it works!!
The above "magic mushroom" software doesn't provide such guarantees (...and insurance payment in case they *do* screw up).
If you ever have critical data on a faulty device, don't attempt any software repairs on your own, and whatever you do NEVER ATTEMPT HARDWARE REPAIRS.
The comment about magical mushroom software.. well, I suppose you could compare that to cars. If you have a Ferrari 612 Scaglietti Special Edition
you wouldn't want to bring it to the local Tom and Harry auto shop. Yes they could fix it most likely... and yes it would be kind of dumb. If you have something worth that much, you want to be sure it's safe. However, Tom and Harry would probably have a few choice words for you if you implied that they don't know how to replace the valve cover gasket on your VW Jetta. Just saying...
I've had several years' experience working with this stuff. No, don't use it to try to get back your company's only copy of the designs for its new flagship product. Yes, use it to recover your photos / FSO gems.