I agree with your advice to younger aspiring programmers and I do think of myself that way. I have no trouble putting in the time to learn another stack. I'm really asking more about how to show a potential employer that it would be worthwhile to take my on as a programmer in a new stack at a pay not too far off from what I'm getting now.
While recruiters (inside a company and those hired by the company) will try to fit you into "buzzword jail", the message to bring to potential new employers is what business problems you can help them solve--the skill that you have in translating a business need into a delivered project or stream of projects. Only a part of that is your skill in a particular stack.
I know of at least one company who hires programmers without Ruby skills, yet everyone at the company programs in Ruby after they join.
Mentally review your career and describe the leverage you have personally been to the effort and what you have accomplished.