Having done a fellowship in regional, I can provide you with a couple of reasons:
1) you won't need a block room because you are so fast at what you do
2) you are exceedingly marketable to private practice groups (ask around if you don't believe me)
3) you join a group with 'something to offer' them instead of being just the 'new guy'
4) ALL your blocks work because you 'MAKE them work' as fellowship will teach you
5) you draw oohs and ahhs as surgery is performed without an LMA or ETT
6) the PACU nurses become your biggest fans
7) the patients 'who got sick from general last time' are your second biggest fans
8) the surgeons who 'thought you would slow them down' become your third biggest fans as they witness how you can provide effective anesthesia at least as fast or faster then GA
9) you increase your group's income (and your partners love you) because they can now bill for post-operative pain blocks that were done in additional to the primary anesthetic (i.e. popliteal block for ankle surgery in addition to the spinal)
10) you place the epidural/spinal that no-one else can as 'the new guy'
11) you learn during your fellowship how to manage complications, how to avoid them in the first place, how to deal with patient expectations, surgeons expectations, etc.
12)if a problem does arise, you have a piece of paper that says you are an expert in regional anesthesia and that does count for something in a court of law
13) you will become facile with ultrasound guided blocks which will probably become the standard of care 'sometime' in the future and your partners who don't know how to do it will ask you to teach them
14) you learn how to place catheter infusions for postoperative pain and how to set up home catheter programs where patients go home with their pain pumps
15) when surgeons ask your group if they are capable of doing xyz you can say yes I am capable of doing xyz and not "gee, I'm not really comfortable doing that, lets just do GA"
16) doing a fellowship will give you a jump on the future of anesthesia