Well, I don't actually have direct experience with an Ospray, but will say that you will find that an Ospray will be a lot more comfortable and roomy than a Sunfish, despite only being about 2' longer (15'8"). The Ospray may not be as "lively" as the Sunfish, but will still be a great boat to sail. My Dad used to have a Beetle Falcon, which was a near sistership to the Ospray (I suspect Ospray design was created by modifying a Falcon) and we had many great sails on that boat! Of course she seemed pretty big to me at the time (he sold that boat when I was 5 years old!) but now look little compared to my DS II.
Advantages to the Ospray: more stable than the Sunfish, won't capsize if handled right. Obviously drier! Will take more than the 2 person capacity of a Sunfish. Less athletic to sail, more relaxing! Has a kicker-pit to clamp an outboard right onto the transom, can't do that on a Sunfish!
Drawbacks include: cockpit does not self-bail, so you will need a boom tent if you leave in water and it rains. Not as easy to trailer as a board boat and can't be car-topped, but still very easy to trailer. Won't be able to sneak into as shallow water as you might with the sunfish, but still can be beached if desired (but not real practical to keep pulled up on the shore between uses, especially in tidal areas).
I used to have a 12' O'DAY Widgeon and enjoyed sailing her all over our coastal area (Buzzards Bay) and into several shallow coves... my DS II could still sail into those areas.... but I feel like a "bull in a china shop" trying to get into some of those tight areas.
Having sailed a Sunfish a few times........ well ,I enjoyed it.... but wouldn't trade my DS II (or my old Widgeon) for one. I think you will enjoy an Ospray if you decide to buy one!