Heat cycles can\does produce dry joints as well as poor soldering.
A close visual inspection with a glass can find most but as said re soldering joints is another, we remove old solder first (tape or suction) before applying new solder.
Beware different solders! lead free, low lead, they do not mix, well & can produce their own problems the newer solders require more heat also.
Also fluxes can be a problem on ALL solder repairs we do we use a flux cleaner,
Nice pics pedrobedro.
There is another thread regarding dust & cooling this helps with the heat\cycle thermal shock problem.
If it's a production environment, soldering is a specialism in itself and you have to apply statistical quality control, stress testing and root cause analysis of field returns, and yes having boards examined with a low power microscope, and having techinicians familiar with the board, fiddling with them and diagnosing faults is part of it.
You could rig up a computer controlled test jig to track down dry joints, but dry joints tend to be a soft fault, temperature dependent, age dependent and the rest, and you would need quite a volume to justify developing a test jig. I have no idea if there are customisable systems for doing this on the market, but if there were they'd be expensive.
In a production environment the question would be "How far do we need to increase the quality and expense of the production methods to avoid these problems to an acceptable extent"?
If you are doing remedial repair of boards in a factory, I'd say you are going up a blind alley if you are concentrating on identifying faults and fixing them cheaply, if the process for producing the boards isn't under proper control and is flawed and if there is no feedback from the remedial process to production. The better idea is to identify faults down to dry joints and other reasons and improve the production quality so there are fewer.
If this is normal field repair, I'd say that that automated fault identification systems are probably a waste of time and money unless the maker provides them and once again they'd likely do better to improve the quality in the factory and avoid the need.
As for dry joints from the point of view of private individuals fixing problens in equipment they own, the advice you've been given so far is as good as it gets. Dry joints are just a difficult problem.