If I keep my boat, I will be putting some time and $ into her to get her ready for the trip. This same money could go towards getting the "Bluewater" boat ready also.
I personally don't have the resources to do it twice, so I would try and do it only once. We went through the same decision making process a few years back when we were trying to decide whether to keep the Catalina 34 we had for local cruising, or get the next boat a little earlier than we needed to. Upside, a bigger better boat to enjoy sooner. Downside, bigger expense for insurance, moorage and maintenance over a longer period of time. Wish I had a goose that laid golden eggs.