I think it really depends on your needs. I f you don't need shoal draft I would advise not to get it.
Our club is located inside a channel that at moon low is only two feet. Shoal draft is very desirable because it means waiting less time to go in and out of channel. Typical low tide is almost 4 feet so many shallower draft boats are not very affected at all.
The next point is that it all depends on the boat and the design. Research the performance of each before deciding. Even die hard cruisers who repeatedly state that "speed is not important" like to have a boat that performs well if possible. As has oft been stated here an extra bit of pointing or speed means you reach your next destination sooner ...
Several examples I have seen at our club. C&C30 mark 1. We have had two with shoal draft version and 4 with the standard fin. The "shoal" version is actually a fin but is a bit longer and about 1 foot shallower. It does not give up a lot on performance to the other C&Cs. In my mind this shoal version is a winner. Other examples are a 1990 MacGregor 26 - not shoal but a swing keel or centerboard or something. The rest of the boats had all finished our end of season fun race and that boat had not yet made the windward mark. Yet another is an ODay 27 with a stubby wing keel. Again the performance to weather is lacking.
I agree with above posters. There are enough used boats out there that it is probably cheaper to sell your boat and buy the same baot with a shoal keel than it is to change your own keel. Then there is the fact that the designers of the boats with shoal keels probably attempted to get maximum performance from that shoal keel as well as stability. A DIY keel mod would always make me nervous. The boat is designed with the keel on it. Unless you area very knowledgable naval architect I can't see chopping off 3 feet to be a good idea in any circumstance.
Buy the right boat for the area. Do the research. Then post your question here about how such and such a boat you have found and how well it is built, performs, etc ...
Looking is the best part!
Full Tilt 2