>>>starting to wonder if I really need a RIB.
That's what it comes down to Stuart... do you "need" a RIB. Many folks (and this forum isn't representative because loads of people do some serious stuff with their RIBs) don't need a RIB but just fancy one. However if your trips and the weather you go out in need a RIB then a SIB just won't cut it. You probably won't die in a SIB but you will end up at minimum speed, soaking wet and bounced about.
But if (like me) you are having a period where you don't want to trail a boat, don't want to store one on a trailer and family/finances dictate modest expenditure then a 3.2-3.8m SIB with 10-15hp gets you on the water for some great value fun/trips.
In this I'm assuming you won't be trailering the SIB? TBH if you were thinking of using a SIB on a trailer then I'd keep the RIB.
If you are considering the daily inflate/deflate with a SIB make sure you have the attitude to put up with it. I treat this 30 min at each end of the trip as part of the trip and almost enjoy it as part of the experience... others find it a chore.
If you do decide to get a SIB in another month or two the prices will be down to winter bargains and £1500-£2000 should get something in very good condition, perhaps a 1-4yr old boat with 4-10yr old 2-stroke in mint condition, transom wheels and other kit.
Here is an example of an outfit to consider...
I'd prefer a 2-stroke outboard but it does come with about £300 of extras in the launch wheels, seat & bow bags plus extra seat.
At the lower end of the budget this was a bargain at £1000... the outboard alone could have made most of that in the usual early summer buying frenzy.