Most currently made liferafts have large water
ballast bags on the bottom of the raft that were developed to "Iceland" standards (were the testing of the new designs occurred) after the Fastnet race
The raft is designed to stay upright in some really horrible conditions when these bags are filled, which they due automatically when the raft inflates.
Many times these rafts have been used and only 1, 2 or 3 people actually make it to the raft and they have survived OK.
You may get tossed around inside the raft if sea conditions are really bad, but at least you'll still be alive.
If you don't need the deck
space for something else and your wife and yourself can launch the raft in heavy weather
conditions and it is still serviceable, I would say just keep it. If it is at the end of it's service
life (usually 10 to 12 years old), then you may want to get a new raft.