Obviously very weather dependent, and depends how much the rest of the crew enjoy longer and possibly slightly bumpy passages, but unless dreadful should be no reason you can't do Poole -> Penzance -> Poole in 2 weeks solely by boat, and possibly Scilly as well, depending on how much time you want to spend in the various harbours along the way - there are some lovely places to explore.
I did Poole -> Penzance (Newlyn) -> Poole over 4 days a couple of years ago in pretty rough weather, stopping overnight at Salcombe both ways, and a pop in to Falmouth for lunch and present buying on day 2. My thinking was exactly as above - if something goes wrong (weather/boat) such that I need to tow it home, I'd just stick it in port for a day rr two and catch the train back to Poole to retrieve the trailer.
My little video of that trip here:
Thinking about this makes me want to do it again now!