M3 organisations stopped being approved in 2004 (I think). From then onwards, only Part-145 organisations were allowed to start-up. (I know that cos I helped start one).
Your friends are alright to carry on until they want to sell-up or move on. I believe they can't hand over an M3 to another owner (post 2004) until it's made up to Part-145, in which case, they will then require a Licenced Engineer (as Chf Eng) to sign off the jobs they do now.
Building Piston Engines has always been a back-room job, not particularly thought of as an "Aircraft" job - more as a component - My apologies for the way that is written, but it shows the way Deep-Strips are thought of. It is a very specialist job (Hats-off to him) but it has been pushed to the back for some reason I cant think of now.
The advantanges of having a Licence over not having one:
a) Its yours - it moves from job to job with you. You may/could be stuck at a place you dont like, with an non-transferable qualification.
b) It demonstrates (world-wide) to others what your level of knowledge is. Would you fly in an airplane with a pilot who didnt have a licence?
c) It may give you some level of 'seniority' over others, if its required - and possibly more pay too!
d) If you had one, you may be able to do the C of A's yourself - without paying some else to do it!
Lastly, It may pave the way for you to expand on your knowledge and into other types - using your (B1.2?) Licence as a starting point. (I have B1.1, B1.2, B1.4)
Hope this helps.