Based on my personal experience... age isn't so much a factor as the three other things you mentioned in your intro... namely wife, kids and mortgage. They will impact on your "mobility" and could mean, depending on your current location, that your options for finding employment might be somewhat limited.
As for the MEIR, it really depends on what it is that you're actually trying to achieve... You say you're happy to do RAAus or instructing, but is that the end goal? or are you saying you'll do that to get to your end goal of an "airline" job? If you're going to be happy instructing, the MEIR can probably wait until you want to move onto G2 or G1 etc... If you're after a charter/RPT/airline type career, then the MEIR is probably something you should consider sooner rather than later (finances permitting). You never know when that "big break" will come along and you'll kick yourself if you miss out.
The 20 hours from earlier would have been helpful, but the missing logbook effectively means they don't exist. Why were you not keeping your own logbook?
As a pilot, your logbook is your responsibility. The only way I could think of to "find" those hours would be to track down your old instructor(s) and get the information from their logbook(s)... I take it that isn't really an option given your bad experience with the previous flying school?
Also, one last piece of advice... make sure that your wife fully understands what is going on... be open and honest, she is likely to end up making a lot more sacrifices than you!