For those of you that visit, or plan to visit this area, there's a slipway in Aberdovey/aberdyfi town, but quite a challenge. It used to be the case that the boat club would also give you a tow across the beach, but my sister who loves there says this is no longer available. There is a small slip at Frongoch boatyard, 3-4 miles back towards Machynlleth from Aberdyfi (you go under a railway bridge to access the slip from the boatyard entrance - aka Smuggler's Cove. It's concrete upper/sand and mud lower and I'd say you need half tide for most boats. You can find it on the 'net here http://www.smugglerscoveboatyard.co.uk/
and it's run by Giles
If you have a boat with relatively shallow draft, the estuary up towards Machynlleth (and you can go some way) past where Springwatch comes from (Ynys Hir) is fantastic. You need fair tides to explore up towards Aberdyfi, but don't let that put you off!
Doc.