Brittany and boats go together perfectly! I bought my SIB with the intention of packing it into the car boot and taking it over, but haven't achieved that yet
If you don't take your RIB over, you will regret it! We have taken holidays there for the last ten years, and every one's been fantastic. There are four things you need to start planning - Michelin 230 (Bretagne), the two Yachting Monthly Pilot books ("North Brittany & Channel Islands" and "West France"), and of course a chart - the Imray water resistant charts cover the area well, but depends on which area you intend to visit.
The character of the coast changes as you go aroung the Brittany peninsula. From the Channel Islands, nestling in the corner of Normandy and Brittany, as you travel west, there is the Emerald coast (St Malo-St Brieuc) and the Rose Granite Coast (St Brieuc - Morlaix) - I've not visited these two areas, but they look good in the books. Then as you head further westwards, you're out into Finisterre - like Cornwall but even more remote! The Abers are spectacular (Aber Wrac'h, Aber Benoit, Aber Ildut) and the Ile D'Ouessant is like the Scillies. The seas out here get quite rough though, even in mid-summer. You can take a day trip by fast launch (60' planing hull!) from Le Conquet to Ile D'Ouessant if you don't get a weather window. Rade de Brest is a huge expanse of water (French Nuclear subs based up here) and I'll be holidaying up here (at Port Launay, up the river from Chataulin) for part of next summer if plans come to fruition.
The Crozon Peninsula is arguably the most beautiful part of Brittany. Huge white cliffs rise out of the Atlantic, but leave beautiful beaches at low tide. Avoid Douarnanez - smelly commercial port (sardine canning factory) and then it gets rough and rugged as you head out around the Pointe du Raz.
Southwards it's a bit flat for a while until you get to one of the best windsurfing beaches in the area at Pointe de la Torche - and it certainly catches the weather out here! Then at pointe de Penmarch it starts to change (Eckmul lighthouse is a major local landmark). As you go Eastwards along the south facing coast, you'll notice the weather getting kinder by the mile. Loctudy is a commercial fishing port, but the next place is Benodet (busy and touristy) opposite Ste Marine (quaint, picture-post-card place) and the river Odet is amazing - no mud banks - just granite boulders on both sides. And incredible for fishing - there's a huge bass population. This is my favorite coastline from here eastwards - Isles de Glenan are my goal for one day (a bit like Keith's Orkney goal!). Beg Meil is a tourist resort. Fouesnant is a major marina and cider capital of Brittany. Concarneau is a historic walled old town, commercial fishing port and marina. Pointe de Trevignon has superb beaches, a harbour, weekly fish market and a popular slipway. Port Manech is one of my favorite places - a tiny harbour at the mouth of the tidal river Aven (like Salcombe a hundred years ago). Then further eastwards there are more islands - Ils de Groix and Belle Isle - both perfect for RIB expeditions.
From memory there are lots of launch sites (and Geoff's boatlaunch site covers some french slipways) but their attitude to boating is different. I don't think you'll find slipway fees, but of course you need an ICC, and the correct home&courtesty flags. And if you wonder why French boats all seem to have auxiliary engines - that's because their government run their equivalent of the RNLI, which IS NOT FREE! In fact they're likely to claim salvage
French launching technique also interesting - they don't like getting the wheel bearings wet, so lots of people use break-back trailers (using the Dave Mallet demonstrated technique of "over the side" - so you may find some launch sites, esp. along rivers, are just a low quay without slipway) or some people just bang on the brakes reversing down a steep slipway (like Pte de la Trevignon) and the boat flies off backwards. Great to watch!
However, you'll probably find that all the imfamous French bureaucracy is invisible because they actually love tourists - as there's hardly any industry in Brittany, it's their major income source.
And of course, the other good things are crepes, cider, and good wine for £2.50 a bottle