Superrav,
The test does expire after 24 months, UNLESS you are employed by a 121 carrier within that 2 years, in which case it does not expire.
I, like you, debated whether or not to take the written. I eventually decided to take it for two reasons:
1. Many major airlines still require it for minimum qualifications
2. It never hurts to be able to check one more box in the hiring process.
My advice : If you plan on being in a regional within the next two years and you plan on going to a major someday (don't forget about UPS and FedEx), then take it. It definitely can't hurt anything!