Mumbai is not where most of ISRO resides
:-) They are scattered if I recall correctly across many places in the Southern part of India, East coast and the rents there are not bad at all. (Certainly cheaper than Mumbai). Also many ISRO facilities provide low cost housing on their campus too.
To your specific point: "hardly any engineers quit NASA to join ISRO", they do not need to. Many of the underlying technologies come from a variety of sources. All you need is a few to be the mentors or lead. ISRO has been around for a long time and so they do have a depth of their own experiences, plus what ever talent is developed locally or by folks who learn from others in stints in Europe, USA, etc. ISRO has also lots of experience since 1950s? It would be interesting to learn how much COTS stuff went into their MOM (% wise...) AFAIK,ISRO folks who do share whatever is possible and makes sense. I have worked with a few ISRO folks and they have shared and published whatever they can. I totally agree 100% with the rest of your observations.
It varies: I mentioned earlier in another response: it is the ones who went back and mentored the bulk of the ISRO folks - which helps explain a lot of recent successes. ISRO has also has had their fair share of mistakes too. As for the $74 million cost - lot has to do with the salaries being a major factor. Same projects can cost different amounts depending upon where the bulk of the work is performed.
Slight correction: a few do go back and actually share what they have learnt. Many of these then mentor or guide many many legions of promising researchers, engineers and techs - so they overall help make an impact. I do not see what that is such a big deal. It is always good to learn from mistakes, does not matter who makes them.
You are 100% correct. NASA has done many a trailblazing projects and they are not averse to other nations for example ESA, trying their techniques or improving upon them. Sometimes NASA also learns from what others try differently.
You are most likely correct. ISRO consults regularly with NASA and many other space agencies and they do share findings and publish many results. There is no doubt at all that they would have checked with previous missions to learn what worked and what did not, so they could all benefit from this.
...which is the real story here. It also helps with speaking tours, etc. All to basic milk as much $$ post the time served.
Sad to see the telegram go - but there is now access to cell phones to a lot more folks (not the 500 million as stated).