We have been full-time cruising the US East coast and the entire Caribbean Sea, South, and Central America. Until now, we have not carried a liferaft. Our reasoning is that although we are "offshore" for days at a time, we are really not more than 200nm or so, and often much less, from an actual shore. And almost always within a few hours rescue distance. We also have a large dinghy on davits that can be immediately deployed. Beyond reliance on a well-found boat, we rely on our EPIRB for ultimate rescue - with the reasoning that we can survive the few hours in our dinghy if necessary to abandon the boat altogether.
We are gearing up to head across the Pacific now, so a liferaft is something we consider necessary for that. Our experience buying one is:
1) They are expensive
2) Don't get a larger one than you need - if you don't have 4-6 people, don't get a 6-man.
3) They are heavy, and a canister really does need to be mounted for deployment because they are slippery and unwieldy to manually deploy. A valise has handles and slightly less weight, so can be manhandled if one is strong and able enough. That last point is worth considering in terms of being in an abandon ship situation. The valise must be stored somewhere it is immediately accessible under any condition that requires you to abandon ship.
4) Storage is an issue. A canister needs a permanent place, which can increase the cost significantly in making/installing a cradle mount. It will be there permanently, and also need to be easily accessible, and these two requirements often conflict. A valise needs to be stowed someplace in a protected environment when not on passage, and they take up considerable space.
5) Rafts come minimally provisioned. Some don't even have water in them. Most assume <24hrs in the raft. You will need a grab bag with supplies for extended time. It is possible to get the rafts pre-provisioned with more, but the costs rise quickly for that, and often push you into a higher upgraded model than you need.
6) Once one has come to grips with the above, the raft needs to be inspected every 3yrs, and this costs 40-50% of a new raft. Assuming you are near a certified inspection business for your brand of raft. So it isn't a one-time purchase. You can forgo inspection, or DIY, but this could void your insurance, or be outside the law in the country you find yourself in and you be refused to leave or enter.
My suggestion is to consider how much "offshore" you will actually be, how far out of range of reliable rescue services, and how well your boat is founded for things like small fires, broken gear, breached hull/thruhull, etc. Then weigh the risk vs cost/storage/maintenance of a raft.
Mark