I think a birthday is a great opportunity for a "big date" involving something kind of over-the-top or unexpected. Here are a couple of examples.
One woman I was seeing was convinced she was plain and unattractive. I hunted around for the right kind of portrait studio, met with the owners, and gave them the mission of making glamour shots that proved she was as beautiful as the way I saw her. I told her nothing in advance except to wear jeans and to bring some eveningwear along, then picked her up in the afternoon and drove her to the studio. "Take your bag and go inside, they're waiting for you, and I'll see you when you're done." Part of the photo shoot involved doing her hair and makeup, so when she came out she was fully primped and ready for an evening on the town (by this time I'd changed too). We went out to watch the sunset at a place with a great view over the water, then for dinner to the kind of restaurant where you want to go when you look like a million. Flowers were involved too, of course. (The photos came later, and they were costly...but very good.)
I did the "go inside, they're waiting for you" thing one other time, this time at a day spa when the woman I was seeing needed pampering more than primping. From the spa I took her to a restaurant where I'd secretly convened all of her best friends in a private dining room.
One year for my birthday the woman I was seeing took a blank-pages diary, hand-inked and hand-decorated the cover and the pages inside, and filled it up with beautiful laser-printed tastefully clip-arted coupons: "Join me for dinner and and evening of music, BBC Symphony Orchestra, March 1st, 7pm" "Night at the movies, your choice, anything from Jackie Chan to English Patient" "Candelight dinner - what can I tempt you with? Seafood? Pasta?" And so on, page after page. Clearly a lot of time and love had gone into it. I married her before she could get away.