Hi - I am a hiring manager for outpatient PTs, and I have a specialty certification myself. At my organization, we do not have an increased salary for staff with specialty certifications, but we do offer an incentive bonus for those who have successfully completed one. With hiring for new positions, I definitely weigh new candidates higher who have a specialty certification (or if they indicate they are preparing for sitting for an exam).
My personal experience is that simply preparing for the specialty certification exam enhances your skill set significantly. Differential diagnosis skills and effective treatment planning are the non-economic wins here. You are able to help your patients more effectively.
I recommend going for it. When the time comes, if you are feeling sleep deprived, perhaps you can defer your test date for a year and roll your application fee back? Something to check into to see if that is allowed.
Good luck!