Lozzin is correct, in aerospace you will find a PHd is generally too specialised to be any use in industry (I am fully aware that PHds have provided plenty of useful research which has uses) but for the individual it rarely is a financially beneficial experience.
My advice, although I understand it is difficult to find work at the moment is with 3 to 5 years experience you will able to start contracting. If you wish to pursue pilot training you should be looking at becoming a contractor at the earlist possible opportunity. To contract you need experience not a PHd.
Quite often as stated PHd holders will only start out on the same salary as any other graduate.
Contracting is the only way you will earn any decent money in Engineering; also you will find the flexibility of contracting can fit in really well with modular flight training. Another thing to consider is when you are applying for contract positions is no one is bothered when you hold a fATPL (where as for permanent roles they are always concerned you will leave for a flying job at some point).
If you do need to kill some time while waiting for a job, at the moment I would recommend a shorter post graduate course (ie: Post Graduate certificate or MSc). I suppose if you do hold a MEng , a MSc could be seen as abit of a sideways step ( or almost redundant). But at this moment a Post grad course concentrating on composites analysis could give you a very good chance of finding employment. Yes you could do a PHd based on composites but by the time you have done that the industry may have realised that Mitsubishi are right and the composite boom will be over.
As for your age, not an issue I have known plenty of people who have been in their early forties when they have gained their first commercial job.