We are 3 couples who have been friends for many years who would like a special place to celebrate a birthday. Golfing and fishing are of interest and a romantic,quiet beach would be a big plus.
Willing to splurge.
Any suggestions?

Brandenton/Sarsota area is really nice. Lido Beach and Siesta Key are great beaches. Lots of golfing, flea markets, oyster bars, shopping (St Armands circle) nearby. I highly recommend it.

What time of the year are you going? Siesta Key is a great beach, one of the nicest in Florida but it is not quiet and there are lots of families there. For couples I would suggest Naples. A beautiful beach, and great shopping and restaurants. Not as family centered and more upscale than most of the rest of Florida. I can't comment on golfing and fishing but I imagine that most Florida locations would fit the bill for those activities.

If you really want to splurge, Little Palm Island in the keys.

http://www.littlepalmisland.com/

Little Palm Island in the keys

Beautiful - YES
Romantic - YES

unfortunately, lttle short on golfing......

Sarasota area has it all. Beautiful Siesta Key beaches, romantic, fun, nightlife, culture, and golf courses galore...

http://playgolfsarasota.com/play-golf/area-courses/

"Sarasota area has it all. Beautiful Siesta Key beaches, romantic, fun, nightlife, culture, and golf courses galore..."
Was that Sarasota or Naples you were describing?

Did not know Naples has Siesta Key?

Siesta key is a great beach. I frequently recommend it . But for what I think this poster is looking for I think Naples is the better choice. Although you could probably never go wrong with siesta key.

Let's see:

Sarasota - Naples

Beaches - S
Nightlife - S
Restaurants - S N
Culture - S
Shopping - S N
Golf - S N
(don't golf but I assume that a dozen golf courses in each city are available to public)
Fishing - S N

Did I miss anything?

Casa Morada or The Moorings in Islamorada are both great, and work well for couples traveling together who want a together, yet apart, vibe. Little Palm Island is very nice, but it is super-expensive. We were there for five days and kind of got tired of how, well, "fancy" it was.

Anna Maria Island. Great B & B's there, romantic and some of the quietest beaches in Florida, great restaurants, plenty of fishing and golf not far. This is a great weekend getaway for adults I think.

Thank you all for the great suggestions.