Going after a startup for innovative work might me interesting and rewarding but it might not neccessarily pay your mortgage.
There are many benefits in working with well established platform and performing maintenance coding.
Personally, I would never accept pay cut for "I'm bored with my current job".
You can always find more rewarding job with higher salary if you really want to.
Just remember you don't have to rush out, and don't let the door hit you in the ass when you leave.
World is actually annoyingly small place and you will end up bumping into your old colleagues and it's much better if you are in good terms with them.
I actually did this kind of move just recently.
I left my old job for a position in a much smaller company with old, almost ancient infrastructure.
One of the main reasons for leaving was the salary, the small company does not have capital/revenue of even /10 of the old company but they pay proper salary nevertheless.
I didn't double my salary by switching but taking into account the layoffs which were foreseeable in the old position, I'd might aswell say I did double up.