I dove Silfra about 7 years ago. The air was about -1C* and the water was +2C*. The operator was Dive.is. It was on the expensive side but they picked me up from the hotel. Good luck on that day - I did not hire a personal guide, yet had a private tour as there were no other divers on that day. The DM was OK. He took photos of me during the dives and carried my weight belt to the parking lot. Everybody craves THAT photo with one hand on the Eurasian tectonic plate and with the other hand on the North American one. On the way back the guide took a longer and more scenic route to give me a bonus trip. But I don't see him now among the team on their webpage.
Was it worth? It depends on what you already have seen. For me, it was the first time with such impeccable visibility and such cold water. The cliffs looked spectacular. If you have been in Mexican caverns or caves, Silfra will not impress you too much. There is no marine life, just cliffs and colours. If most of your dives have been in a local quarry, then Silfra will be an adventure.
Apart from cold conditions, it is a benign place, almost like a pool. The park regulations did not permit to go deeper than 18 m or enter the overhead area on the bottom. It is a short distance even if you go all the way to so-called "Laguna". So don't hurry, take your time, use your gas. Stay in the "Cathedral" section as long as you can.